I've only used Mediawiki on a few sites. The forum at
http://www.mwusers.com/ was what I used to answer all my questions. It's been a while since I had an install but one of the first things you'll probably want to do is harden it up against spammers with a good captcha like recaptcha. There was a way to make it so anyone adding an url has to type in the captcha and this helped a bit.
Also if I recall correctly php APC made a big difference in performance with Mediawiki.
Mediawiki is very bulky but it has a lot of capabilities. It could be overkill if you are just planning on having a couple dozen regular registered users and contributors.