Don't edit before you've finished the first draft
As you say, it's best to let the first draft out on the page and postpone worries like structure and size to the editing phase.
So whatever I say here, don't worry too much about it until you have your first draft and are ready to go into editing. (You'll likely strip down, rip out and restructure in editing anyway... First drafts are, as has so famously been said, shit...)
Make it attractive to the reader
Story structure is a tool for making the novel and the plot move along and to make it attractive to the reader.
In one sense this means, you can make the book as long as you like, just keep the reader interested and attracted every step of the way.
The big question is, how do we do that? How do we know where to place our plot points to keep the reader glued to the page? How do we know how long the acts can be before the reader gets bored?
We can of course use beta readers, but maybe only once or twice per work, so we'd better use all available knowledge to make the novel as close to "exciting all the way" as we can get.
And that's a balance between structure and "exciting on the page". Usually, a good book, movie, or stage play is a bit loose with the structure in order to make the scenes work.
What does structure really do to the story?
Being off on the structure can have several effects.
If the story is long but not exciting on the page, it gets boring and put down.
A story that has its first plot point halfway in is usually a sign it has been badly structured. You're going to feel that the end is abrupt (this can be seen in some movies and stage plays.)
A longer first act will likely also feel like the beginning is dragging on and never cutting to the chase...
If the acts are too short you could be brushing over important parts of the storytelling.
If your first act is too short it could mean you're skimping on establishing the real world (maybe the world at stake or the world that must change) and its characters, leaving the reader with less investment in the world, characters, and ultimately the whole novel.
If the middle acts are too short it could mean both character development and setting aren't used for maximum effect.
Middle acts that feel long or boring (some call them sagging middles) usually feel that way because character and plot development isn't optimal. Both your story (the external story) and your main character (the internal story, character arc) need to come from a defined beginning, then change noticeable in the middle and arrive at a defined ending.
The only exception is if your main character is a hero or a super (they already believe in the truth of the story and follow a flat or testing character arc) then they change other characters (noticeably) or even their whole world, after having gone through hell themselves... (Katniss, anyone?)
And likewise, a final act that is too short will likely come off as an abrupt and possibly less meaningful/impactful ending. "What do you mean 'and then they killed the villain'? If it was that easy, why did I spend all this time reading the other acts? Come on!"
A long final act, on the other hand, will probably come off as dragging out the end and could be caused by not ending subplots before the final clash between the protagonistic and antagonistic forces.
Rules for novel size
Your work will be judged by readers on external things like cover, font size, and page count (maybe a bit less so in an e-book) so a publisher will also have notions on novel size.
Especially if you're debuting.
The most common notion is that genre and audience are important when determining the min/max length of a novel. For instance, a children's book could never run 200k+ words. A Sci-fi/Fantasy book might if you're introducing whole new worlds with unusual physics and culture. While urban fantasy might not have to explain a whole world and could get away with fewer words.
It's not impossible to get a large book published, it's just going to be harder.