Goto this thread first and get the stock ROM for Bell:
http://forum.ppcgeeks.com/showthread.php?t=27123
Then activate the phone. This should wipe any weird crap the previous owner may have done and reduce problems with activation. Once you have it activated, start reading through the stickies and make your own opinion as to what ROM to upgrade to and whether or not to upgrade the radio software.
If you DO decide to go with WM6 or 6.1, I would recommend updating to 6, THEN to 6.1 to avoid hassles. I took my old Apache to AKU 3.5, then, WM6, then WM6.1. However, on my new Apache, when I tried to jump from stock ROM to WM6.1 I had many problems. So I hit it with 6.0 FIRST, then went to 6.1.
Hope this helps a bit.