Can you invite people to the bachelorette and not the bridal shower?

It is absolutely ok to invite people to your bachelorette party that won’t be invited to your shower, as long as they are invited to the wedding.
And no, there is no rule that says you have to invite the spouses of the groomsmen to your shower

Ultimately whoever you want to invite, that's who you should invite. That being said, to your specific questions:

Because you are not inviting guys to the shower, I think that is fine and they can def come for the bach party (In contrast, I had my two best guy friends at my bach and my bridal shower, no other men for either event.) For the girl who wont know anyone at the shower, I would still invite her. She can make the call on if she wants to come or not. I think it would be rude to not invite her.

For gf/spouses of groomsmen, that's an all or nothing if you aren't super close with any of them. Either invite them all or don't invite any. I personally didn't invite any of them because my FH has a lot of women in the family so my bridal shower guest list was pretty large as is and adding 9 other women wouldve been too much. I see them all at least once a month, but none of them were offended

Yes that's fine.

The only hard and fast rule is that everyone invited to pre-wedding events must be invited to the wedding.