Sounds like you’d jump right into your major at Amherst and still have space to explore other interests. And yes there are a lot of paid research opportunities (abroad, during the school year and in summer/Jan break), though the SURF program is I think only for first and second year students. You might check if that’s important.
The Core seems like a transfer killer to me, even if you don’t have to take all those classes, everyone else will have and only transfers won’t have? It’s such a key part of the CU experience.