So the question is pretty straight forward. Let's say a CC group is in the middle of a campaign and the Imperial side has maxed out their bases. Does this mean when they win at an unoccupied system in a normal assault it remains simply unoccupied? Do the Imperials gain the resources there for even one turn or no?

You only gain resources from locations with bases.

Simple as that.

It will have to remain unoccupied, until such time as the Rebellion destroys a base, and you win again , and pay to build a Base there.

I see.

****.

Hopefully the rebels will also tease the empire by saying

"all your base are belong to us"

If the planet you just won has greater resources than one of your existing planets, can you remove a base from another planet and build a new base on the new planet instead?

There is no mechanic for removing bases in the rules, other than Destruction.

In fact, if you play with the Poster + Stickers as intended, all you can do is place a Destroyed Sticker on a Base when a Base is Destroyed - Stickers, and thus, bases, are never removed otherwise.