It all depends on one big factor.
Can you be co-parents with your stb-ex husband? Can he put the wellfare of the children first and be part of the team of parents who does what's best for them?
If the answer is yes, then this can be quite simple.
You start off by putting topics on the table to discuss. Not suggestions, demands or wishes. Topics, on which you can have a dialogue together and work out what the best way forward is.
As soon as you start off the conversation with your ideas, wishes and demands, you'll bump into resistance and defensiveness, and that won't get you anywhere.
So rather than saying "we need to figure out which one of us moves out first", you'd say something like "we need to discuss housing. What are the pro's and con's of the different options we have".
Think questions rather than statements.
It would be great if you can start off with a foundation of "we're figuring this out together. We'll get some thing right and we'll also make mistakes. That comes with the unknown territory. We assume we're all here to do what's best, so mistakes are no ones fault. Just part of learning".
If however that above scenario is completely unrealistic - which is likely because otherwise what would be the reason for getting a divorce - then you need a completely different approach.
You need to be as prepared as you can. Get legal advice. Talk to a child psychologist to get advice on how to tell the kids. Surround yourself with people who can give good objective advice that won't be cast aside because of emotions or impulses. Get a mediator to help you work out the practical side of things.
Make sure you're prepared for a nasty divorce. Great if it turns out fine, but best to be prepared so you won't be caught off guard.