welcome kent,
i'm fairly new to this forum, too. i recently installed a new exhaust system from the down pipe back. i went for a 3. 5" system without a muffler, as i like the exhaust note.
one thing i learned from that experience (and would definitely recommend) is to spend the time and a little extra money to find a place that deals in commercial big rig/industrial/marine exhaust systems. not only are they used to dealing in big tubing, they will also typically use a band-style of clamping.
the standard automotive exhaust u-clamps are cheap, but crush the tubing a little, end up rusty, and make replacing a section of pipe (when necessary) more difficult. the industrial band clamps (not sure of the trade name) don't crush the tubing at all, are less likely to rust, and make taking the system apart (when necessary) a breeze.
just my 2 cents...
roy