WordPress.org

Does it work with WP Super Cache (or other caches for that matter)

No, but you can simply add the URL of the page where you use the form to the ignore list (at least with WP Super Cache, tested with version 0.9.9.6): 1. Go to WP Super Cache configurations in WP Admin. 2. Go to the advanced tab. 3. Scroll down to where it says "Add here strings (not a filename) that forces a page not to be cached. [...]" 4. Add the path of your page/site.. eg if it is in http://yourdomain.tld/contact/ then "/contact/.*" will fit).

Example: I use the SCForm here: http://blog.foaa.de/about/, so i added "/about/.*" to the list, cleared the cache once and it worked like a charm.

How many fields i can use in my contact form ?

As much as you want and common sense dictates .. surely i didnt test with more then a "reasonable" amount..

How can i use SMTP for sending the contact form mails ?

This plugin uses wp_mail() instead of php's mail() so you need (another) plugin which modifies this method. I used WP-Mail-SMTP ( http://www.callum-macdonald.com/code/wp-mail-smtp/ )