Wordpress+WP-E-COMMERCE+VARNISH

[Emiliano Barrionuevo]

Hello. This is my first Varnish setup I plan to do. The question begins 
with the setup:

Webpage (Wordpress+WP-E-Commerce) Testing/dummy site www.ilomilo.com.ar

Homepage | No cookies needed, daily updates, SSL
Products Page | No cookies needed, weekly updates, SSL
Product Page | Includes button to add to cart, need cookies, SSL
Checkout - Transaction Results - Account | Needs cookies, SSL
1 gig of resources (images & other media like pdf)

Server configuration (planned):
Intel(R) Xeon(R) CPU X5460 @ 3.16GHz, 3 cores, 1.75 GB of RAM, Max of 3 
GB burstable
Linux 2.6.32-042stab044.17 on i686 (CenOS 6.2)

Main site
Varnish (ver. 3.0.2 revision 55e70a4) port 80, 443. - Nginx - PHP-FPM+APC
Local CDN
Nginx

Questions:
How can I tell Varnish to enable cache on certain url and let pass 
cookies on others/rest of the site?
Having 500.000 visits/month what's the best practice for cache purge?
How can i configure varnish and nginx, one serving cached pages and the 
other (nginx) serving static content like images ON THE SAME MACHINE. I 
have 2 spare IP address.
I have HyperCache plugin for Wordpress, it generates static files of the 
site and sends it to nginx to serve. APC also do its work. Should I 
disable HyperCache and let Varnish take care of the PHP content?
More on HyperCache on http://www.satollo.net/plugins/hyper-cache