1- No that part of the game was changed ages ago for some reason. Don't know why tbh as that was the best/easiest way to attack and defend bases in the later game. They used to also take over any airfields you captured making it easier to defend them.

2- Not sure what you mean fully but you can decrease enemy at a base by wiping some out and coming back again and again. Check the map then click the outpost to see if its weekend/decimated. You normally find a base stays decimated if its captured once then taken back by one side. For some reason the AI don't often garrison the bases properly after taking it back, not always but 80% of the time.

3- Don't know if that's possible tbh.

There is a V1.9 available on gifthub with the old mode you seem to have played (nato points and more missions) but I couldn't get it to work. It keeps saying ace is outdated although that could be something I've done wrong with the download. The video below has the link to it as that was a much better game mode IMO.
https://youtu.be/fDBAWZtqqF0

Still a beta I think but Barbolani seems to not be doing anything with this mod now so might be worth trying this.