I hopped on Discord with Rob earlier and hashed through a bunch of rules questions. I might figure out what set of lifepaths you're inclined for before he posts the rules, but not generate until the new rules are up. There is some balancing to help factions that don't have 2d10 lifepath event tables to get extra skill points to make them more attractive for example. Also, total lance personnel (pilots, techs and doctors) will be capped by Leadership.
Here's my understanding. The old campaign is done. If you already completed retirement checks, great. If you'd like to make retirement checks, cool. If you make retirement checks you would need to try and retain anyone you would have as if the old campaign was continuing.
Mike was going to buy two new mechs. Didn't happen and while I would let him if he wanted to, I expect he'd rather bring over one of the current custom mechs.
For XP as you're bringing over an existing pilot, yes, you should figure out the XP they earned. If you want to spend XP before bringing them over, you can do that too.
I agree once you roll, you've rolled. If you want help with the character creation process, let me know and I'm happy to work with you on it.
Hope this helps.