Is adding new ideas to a chapter after finishing it a bad habit? It's my first time writing a novella, and English is not my native language. Is it ok to edit my chapters many times to get a perfect draft?
My general rule is that you should stop editing a work when you are no longer confident you are making it better. That doesn't necessarily mean you might not come back and edit it again later --after more time has passed, or after you've gotten feedback.
In the larger picture, you should stop editing your work if it gets to a point where endless revisions are threatening to prevent you from completing the work and submitting it for publication.
It is perfectly possible to add extensively to any work, or any part of it, after you write the first draft. Many writers have made major changes to works in the revision process, including changing the basic theme, shifting which characters are the main ones, altering large portions of plot, etc.
This takes up time. This may be unavoidable, but there is also the real peril, in that there are many writers who endlessly revise a work, never to go on to another, and never to publish. However, that tends to be people who revise a work twenty times. (If you find yourself endlessly revising, you may want to recruit beta readers.)
For your first question, it depends. If the idea you add expands on the chapter and makes the story better, then it would be good to add it. If it interferes with the flow of the chapter or makes the chapter too long, then maybe put it somewhere else or give it its own chapter.
As for editing, this is perfectly fine and this is good. Editing is something you'll have to do eventually, so getting it done right away is great. Although, I would recommend finishing the story first before any major editing so that you don't accidentally edit out anything important.
Well for your first question, I'd say yes and no.
The reason I say yes is because you could do this. It's as simple as that. Adding more to an already made chapter is a perfectly ok thing to do, I've done it a few times myself, actually. As long as the chapter still makes sense after you've finished editing it, and the next chapter is still smooth, that is a perfectly good thing to do.
But the reason I say no is because if you don't do it right, you might just ruin it.
What I mean by this is that if you don't edit the chapter in a way that makes sense than that chapter, well, it will stop making sense. It will become very confusing and readers will put your book down right then and there. And the same applies for if you don't make the transition into the next chapter smooth. What I mean by this is that if you write two chapters and one ends at a certain place and the next starts off at that place, you can't ruin the balance by adding too much more onto the first chapter.
For example: Right now I'm writing a book that I'm calling "Last" (This originally started off as a school assignment and I know that there is already a different book called "Last." This name is still in progress, I'm just having trouble choosing what to call it). In chapter 10, the main character and two of his friends break into a facility to save their friend who was captured and is being held there. The chapter ends with them standing outside the fence that leads to the front door, and chapter 11 starts off with them inside the facility, scoping out the place to see how they can best make it to Emily (the friend) without getting caught by the guards.
If I were to go and add on to chapter 10, making it so that it ends when they find Emily's cell, and then start chapter 11 off with them just making it into The Facility, that wouldn't make any sense. That means that I would also have to edit chapter 11 so that it starts off smoothly where chapter 10 left off.
If you do all of those things, you'll be fine!