1. No. You need to upgrade manually, however the binary for the new release is available.
2. It should be fine, APC for 64bit is available.
3. You need to get them from their source package, for now.
4. Depends on how many concurrent requests for dynamic content is served and the same of the responses. You can try anything you want.
5. epoll, "best" on linux 2.6 is "epoll".
6. You can save some CPU recycles by using level 1, or get a little bit better compression with level 6.
7. Use a rewrite rule to test value of "Host" header is the easiest solution.