Good for you Jon!
There are only a handful of removeable fin systems:
FCS, Futures, Red X, O'Fish'l, Lok Box, Pro Box and 4WFS.
Arguably FCS is the most popular fin system in
new surfboard construction. They offer the most templates and are pretty easy to locate boxes and fins. Futures seem popular in wakesurfing also. I swear by Futures, but I also think the best fins that Futures offers are pretty pricey. Pro Box is very customizable and allows use of FCS and Futures fins. Lok Box is probably the easiest to install and offers some minor adjustments. 4WFS offers all kinds of adjustments but the installation process is cumbersome. Matt S did an install here on WW.
Futures Fins http://www.futuresfins.com/installation.php
4 way fin systems http://www.4wfs.com/index.php?p=install-points
Futures and FCS installtion guides in PDF format http://www.foamez.com/page_2.html
Foam EZ is a bit pricey, but has most common supplies. Fiberglass Hawaii is a good source as is Fiberglass Supply. A quick search on a search engine will pull them up.
Also if you search for the fin system manufacturers almost all of them have links to reps or sell online. These sites also tend to have fin selection guides...although, you'll need to interpret them for behind the boat.
Hope that helps some.