Hello Don,
I'm flying a turbo 3rd gen 13B in my Cozy IV. My engine has high compression rotors (9.7), a Turbonetics turbo and a Tial auto wastegate. I boost up to 44 MAP (5 psi) on take-off. My setup, though on a pusher, is similar to what you describe with the turbo output going under the engine to an intercooler, TB and manifold on the cold side.
I agree that more power is never a bad thing. It gets you to a  safe  return height MUCH faster and makes it easier to fly high and over weather. Feels good too :)
>Which turbo should I use
After blowing three stock turbos, one of which was an expertly rebuilt T04 Hybrid, I wouldn't even dream of installing anything but a new custom ratio Turbonetics T04 with auto wastegate. (my 4th turbo with around 65 hrs on it with no problems).  Details of my turbo install are on my web site at http://canardaviation.com/cozy/chap29h.htm - search for turbo.
>I read about a N.O.oil line solenoid to the turbo bearings
Sounds like a good idea, (especially if you install a stock or modified stock unit). I was down 2 quarts and trailing smoke after blowing a turbo at 11000' 35 miles from home. I'd guess I had 1/2 hour or so before being out of oil.
>What is the ideal situation with a waste gate?  Full open or not, or, or?
You need one, and the stock one is not enough. Get a Tial
>What size exhaust is optimum?
Mine is a 2.5 inch straight pipe with an attempt at an augmentation exit. No muffler. With the engine at the back there isn't room, and you really don't need one.
I have one TB. I forget the size, but it's stock ford mustang, I think.
I'm using four stock 13B turbo 550 injectors. Idle's smoothly at 600 rpm.

It made a big difference when I went to an in-flight adjustable prop. With the fixed pitch I would occasionally hear the pop pop of pre-detonation on runup. Its rather like flooring an old car in high gear while going up a hill. Moving to a finer pitch is like changing down a couple of gears. No more detonation sounds.

Hope this helps.
John Slade