[support] Drupal 7 and Page Caching

[DTH]

I'm currently setting up my first big Drupal site that requires
caching. The vast majority of the traffic is anonymous, so we can
cache full pages. Currently, for a somewhat smaller site on D6, we use
Boost, which works pretty well. The only other requirements are:
ideally have relatively smart expiration of caches (as well as
clearing cache on page updates, things like updating related views on
node updates) and it definitely needs to work with Domain Access
(shouldn't be a problem I don't think for most caching solutions?).
Also, caching that can also works for logged in users would be a
bonus, but unnecessary. (ie. it would be nice if things were quicker
for admin users, but that's lower down the scale of things)

What's the easiest/safest/most foolproof/most common way to cache
things on Drupal 7?

Drupal 7's native cache - stores it in the database? Would ideally
want to avoid the database entirely.
Boost - seems to have slowed down a lot on development for D7?
Varnish - have never used but this seems the most common D7 way -
anything to be aware of? If Varnish listens on port 80, and I also
have non-Drupal pages on the same domain, how do you pass through
things so people can access example.com/nondrupal/page? Do I need a
reverse proxy or will Varnish pass it through itself? If starting from
scratch, which version of Varnish should I use?
Memcached - presumably am fine to use this alongside Varnish/Boost for
logged in users. Do I just drop it in and use it for all systems
(caching, sessions, locking)?