I'll answer the best I can:
1) It depends on the scores. Unless you've already taken both of them and gotten near perfect scores on both, I think you only need to turn in one. If one is better than the other then turn in that one. I guess it might help slightly to have both, but probably not much.
2) If you take the ACT then subject tests are optional. If you have good ones send them and they'll help, otherwise don't worry about it.
3) You don't need to send in the SAT II's regardless if you have the ACT. I'm under the impression that you self report AP scores when applying (so they have no way of knowing that you're even telling the truth), and thus they barely look at AP scores. They do test similar materials to the SAT II, but the SAT II does a lot more in the admissions process than an AP test, so if you can do well on one I think it's definitely worth it. I've had people tell me SAT IIs could be more important than SAT/ACT (this is an opinion).
I've never heard of this "formula". Did you read this somewhere? It's possible they recalculate your test scores into some composite number; however, they insist that they use a holistic process, so they definitely don't use a formula for overall admissions.