I have a Pro TL set up with the AE finder and WG401 grip, works like a champ. I tried the WG402 but found the grip too small for my medium-sized hands. I also have an RRS QR plate for tripod work. The AE finder has three settings; Average, Spot, and A/S where the camera picks the metering pattern based on the light. It works very well.
I also have a Pro with WLF and crank. This is very fun to work with, but I either have to find a grid screen or a bubble level because my horizons are always tilted a few degrees, most noticeable when I'm shooting boats on the water. I have a strap on this one, I took the clips from a couple of Mamiya hand straps and put them on a Crumpler Industry Disgrace strap. A 55mm lens lives on this body.
For lenses I have the 35, 45, 55, 80 f/2.8, 150 f/3.5 and 210. If weight and cost are considerations, skip the 80mm f/1.9; the 2.8 is a fabulous lens.
I have several backs and way more inserts than I will ever use. If I am expecting to work fast, I preload several backs so as not to have to piddle with inserts while I'm moving around. If I'm set up on a tripod then I just use two backs and several inserts.
A further note about the strap clips... There is an Op/Tech strap that claims to be compatible with the posts on the 645 Pro TL. It isn't. I tried. You'd have to get a round file and open one of the holes.
All in all, a great system. And cheap!