Can I mod my team competitively with the modules store?

Like what jpbrunel says, try splitting where you put your cantina refreshes, put at least a full refresh into mod challenges daily or it'll take a very long time playing catch up.

On the bright side you have droids, which still aren't in a bad place. They won't hold your position as well in defence, but they're still effective in attack.

Do carry on farming b2 - good choice. Do buy jawa engineer shards from the guild store every time they appear.