If you have the cash up front, I'd agree with Sieg on getting a full chassis system. I pieced mine together over time, but then had to put the whole project in storage for three years. I wish I had held off, saved up the total and got exactly what I wanted. My car is still killer, and is incredibly composed and stable, whether in tight turns or getting rid of speed after a 150mph straight. The T56 is a tremendous transmission. It shifts great, is super strong, and for me, the close ratio version makes it plenty versatile. I literally get 28-30mpg on the way to the track and then pass everything that isn't a properly driven Gt3 on the track. It's great!
I have the Speedtech torque arm. I don't have enough experience with other suspensions to provide you with any comparisons, but I can tell you that there is no comparison to leaf springs. No wheel hop, it just sets and goes (with perhaps a little wheel spin
. Even when sliding a bit, it feels completely composed and manageable, my chassis never feels overpowered or stressed. Coming to a stop is a straightforward affair, nice and composed there, too. I really like the Speedtech product. It was relatively inexpensive compared to other options and for me, pretty easy to install and required no cutting of the floors, etc. I would say to go with triple adjustable shocks, though. When I started out, I was advised against it (too many settings), but it turns out there's a ton of information these days, and if you are willing to use the scientific method, you can really make your car handle.
Mine's still a work in progress, but there you have it!