A separatist faction that GAR can fight against

I think that there should be a separatist faction because it will make this game more fun because this game is missing some action . So the devs could make a spawn point for them and there should be points around the that you can capture for in game credits.

I feel like your just describing raiders. The raiders provide pretty much the same thing. Plus the raiders already have b1 and b2 battle droids

There is already like CIS and SER, and an official raiding group is planned.

As stated above, a large-scale raid group is planned to be built. An OFFICIAL one.