ssl with boost and securepages module
Should I use securepages?


No. The best practice these days is to just go with https for the whole site.  


How do I go about caching my https content?


On a normal site, the https wouldn't matter, you can cache static content regardless of how encrypted it travels. BUT. The caching questions are legitimate because it is an eCommerce site and with that (by default), even anonymous users will have a session. Most default caching systems do not work with per-user sessions, unless you use something like authcache.