True in theory but harder in practice. A Goliath or Van Saar gang using only the old minis will have trouble building an actual gang from their house list to start with. Not impossible, but you'll need multiples of the same model.
Depends on gang and minis. Most will be "legal" once you have access to the full trade post, but you might have trouble equipping your starting gang from the rather restrictive house lists. Also, having to spend a lot of creds and trade post actions buying the minis you have will make building...
Should be post today (so there's a chance) but I left for vacation during this weekend. Probably a combination of "rationalization" of the service and holidays.
I do look forward to a new toy, but spreading the joy around and into 2020 is OK with me.