Hey! Sorry for such the late response! It’s been quite crazy with the coronavirus!
So, I am doing a BS in economics (finance concentration) and a BA in Computer science. Essentially, the economics department deters any BAs, despite them offering one. The BS is overall more robust and employable. With computer science, it is similar; however, BAs are more encouraged for those double majoring with CS interest.
Basically, the way I see it, is BS is your “degree” and a BA is a nice “add on” when it comes to STEM fields (which both are). I do not plan on entering tech but feel I can benefit from CompSci in finance. It’s possibly to do two BS though, if you wish to! I am mostly doing a BA because I’m also fitting in a certificate (Markets & Management) so it’s a pretty tight schedule and BAs are quite fewer classes!
When it comes to your second question, the two majors have the exact same math prerequisites (which helps). There are some electives that crosslist between the two departments but I’m not taking any Bec most of my Econ electives are finance Bec my concentration. Overall, the big thing is the math prerequisites. Then, you’d have the CS and Econ core to go through separately and the electives.
When it comes to AP Stats, it basically will not help you placement or credit-wise but I’ve found myself better-off with the knowledge from it going into Econ 104, math classes, etc.