Preface: What the Snowflake method [SFM] doesn't provide. I have added this after my main post, to make this explicit.
In SFM Step 3, you decide upon your main characters motivation, goal, conflict, and epiphany. You provide a one-sentence story line. Clearly these notes do not determine your character's personality, if they are good or bad, if they are funny, irritable, kind or mean. "Motivation" might explain they are inherently good or selfish, but this is still not enough to make your character likable, human, compelling, etc. Unfortunately most people's "motivation," hero or villain, is given as shallow: For the hero: "They are her family thus she must save them," or for the villain, "He loves power and money". These shallow one-sentence motivations also don't make your character seem real.
In SFM Step 5, you write a 1 page character synopses to "tell the story from the point of view of each character." At the standard 250 words per page, this isn't much, and the point here again is plotting, making these stories fit together. It is not actually character development, other than making decisions for a character about what they do next. In any highly condensed representation of your story, you don't really figure out what makes your character tick, the incidents in her life that shape who she is when the story begins. Revealing these things in the course of the story, through conversations and reactions to others, is part of what makes the character feel real.
In SFM Step 7: You expand your character descriptions into full-fledged character charts detailing everything there is to know about each character. Birth date, description, history, motivation, goal, etc. "Most importantly, how will this character change by the end of the novel?"
The "History" component would help flesh out a character, explain why she is where she is, what traumas have led her to where she is, but the SFM gives short shrift to this, lumping it in with her birth day and "etc" in a "chart".
History is the soul of your character.
Her childhood dreams and aspirations shaped her, and are largely instilled in her by those that raised her. Her childhood traumas, losses, disasters and deaths shaped her. Some of these are what make villains and make heroes. The history that shaped her, and how she responded to it, is what makes her "real" to people.
SFM Step 8: Planning and plotting of scenes. All fine, but focused on plot, and still no history of the characters, so you are inventing that on the fly.
SFM Step 9: Optional, a summary of your story.
SFM Step 10: Write the first draft and solve small scale problems.
The Snowflake method doesn't help you develop "real" characters.
That is my conclusion of this preface. Now the OP asks, "What are the right steps to take, bases to cover, to ensure you have successful characters at this step?"
Because the SFM doesn't include a focus on a "successful" character, you need supplement it with a step 3(a), "Describe the driving personality points of your character, with incidents that justify each." if she is ruthless, why? What happened to her to make her that way? If she is fearful, or brave, or promiscuous, or chaste, or shy or bold, or funny or not, tell me why. If she has never been in love, why not?
The SFM guy says in Step 3, "Characters are the most important part of any novel," and in Step 5, "Editors love character synopses, because editors love character-based fiction."
Yet the SFM pays little attention to getting readers invested in the characters, showing their emotional makeup, the emotional events that shaped them, and why they are the way they are. It is more suited to an action novel, which can be fine fun. But although 007 is fun to watch, he's a cardboard character. We don't know how 007 came to be an agent, learned to kill, etc. He's pretty emotionless. By comparison Jason Bourne is a much more emotional character in the same vein, and feels more like a real person because of the emotional non-action scenes in those movies.
In my work, I consider a "successful" character to be one the readers feel like they know, so by the time they are halfway through the book their reactions to the character's actions are "yeah, that makes sense." A successful character is one the reader understands and is not neutral, the reader either actively likes them, or dislikes them. To accomplish that you need to make them human.
IMO, a simple list of traits (as I think the SFM encourages you to develop) doesn't work, for the traits to be coherent (not contradictory) you need a "why" behind them in the history of the character.
This is what was in my mind before writing the post below; to make your character "successful" you must do a bit more than the SFM details, or at least invest the character creation steps 3 and 5 with a greater focus on their personality and a history of how it came to be. A laundry list of traits does not make a person, nor does it make them likable or unlikeable. Their history results in their traits, and their actions towards other characters (and the reactions of those other characters) make them likable or unlikeable.
It doesn't make too much difference which method you use; good characters are good characters, and have been since before we began analyzing stories and coming up with templates to write them. That is all the Snowflake method is, one more template, like the three act structure, or Shakespeare's five act structure, or Brandon Sanderson's videos on character, etc.
What you want in your character is something the reader will have a strong reaction to. It doesn't have to be "extreme", but it should be obvious: They are kind, or they are mean. I always make sure my characters, all of them that are mentioned in more than one scene, have something they are very good at, and something they are very poor at.
Your hero(es) and villian(s) should be proactive. They have problems, and they take actions in some way to solve them. Others in the story can be reactive, but not the main ones.
If you want your hero likable, she should be liked by other characters, generally for reason, they are helpful or understanding, not cruel. The opposite if you want a character unlikable, she should be disliked for a reason, she is rude, cruel, murderous, careless, or otherwise selfish in some manner.
Most cases of "likable" and "unlikable" involve the extremes of "other oriented" or "self oriented", in the extreme case of unlikable, the villain has no care for anybody but herself, and will kill, or let others die, or ruin lives if it poses no threat to her, and brings her any advantage. However, some of the traits that make her unlikeable are advantages for success in politics, business or crime, or any kind of large organization (even a charity), where a little backstabbing, rumor mongering or unethical tactics helps one get ahead.
In the extreme case of likable, a person is so "other oriented" that she would sacrifice her life to save another. Slightly less extreme is risking her life, or sacrificing her time to help.
People can also be liked for their humor, or for their skill or expertise. In writing, you generally don't want to hit the extremes except in extreme circumstances. For example, Sherlock Holmes is not a very likable character, but we like him anyway, and he is written to do far more good than harm. We wouldn't reject him as a friend.
That is why my main characters have something they are good at, to increase their likability, and something they are not that good at (that matters and affects the story), to help humanize them and make them not relentlessly good, or good at everything. Preferably (to me) the good thing comes at the cost of the bad thing; but I don't consider that a necessity. Sherlock's detective skill, for example, can come at the cost of social skill.
It takes more than just a "high level of want" and obstacle. You need the reader to also want that for the character, because they believe the world will be a better place for everybody if the hero gets the thing she wants, and the villain doesn't get what she wants.
Having said that, what she wants doesn't have to be world-changing, she may want safety for herself and her kids. In the movie, Erin Brockovich wants justice that will result in care for the people of the town, fathers, mothers and kids that were poisoned. That's what she's fighting for, not to take over the world, but right a wrong.
Finally, I'd disagree with the notion that there must be a high level of want for anything specific. A coming-of-age story can be great without any particular villain, without any particular goal for the hero, just a series of events and problems to overcome that end up changing who they are. Little Women is still enjoyed by thousands every year, and the girls are just growing up and having their life experiences, good and bad.
On balance you want your heroes likeable, and those that get in their way unlikeable, and vice-versa for your villains.