Melvesreef is a great place for info (as you've found)
There's also an endless thread on RC in the DIY forum titled something like
"acrylic fabrication questions, I can help" by Acrylics. Great info there also if your patient enough to wade through it. If you do take a look at that, follow the split threads back to page 1 of the original and there's a very nice walk through on making a tank/sump from scratch.
For supplies, if you are in boston anytime (weekdays 9-5ish) Altec on B st generally should have anything you should need (except acrylic tubing).