May I wish you a warm welcome to the CameraLabs forum.
I'll leave specific advice to those more familiar with the system but if you check out this site's lenses page
you can find links to listings for both Sony's and Sigma's lenses for the Alpha system. And then there's the A mount lens database
which gives you information about all those legacy lenses you mentioned. Good luck.
Oh, and one thing that did occur to me as I read your post is whether you wanted a 200mm lens or a lens that offered the field of view that a 200mm lens would offer on a full-framer? The difference is, of course, down to the Alpha's crop factor.