What do you recommend if all of my pages require a user to be logged in, and the pages each have user specific stuff on each page's header, e.g., a my account link, an icon showing the number of items in your cart, etc.

Server side includes might be a simple solution for this:

http://joshuajonah.ca/blog/2010/06/18/poor-mans-esi-nginx-ss...

It depends on your DB schema, but I would recommend taking a look at Johnny-Cache, or django-cache-machine for queryset object caching.