Welcome aboard mate.
Your first mods should be an upgraded and decatted exhaust, GTA air intake conversion and after that an ECU remap.
Make sure to get the GTA intake done first as it's the cheapest mod available costing around £15 brand new. Then go with the exhaust, that'll set you back a few hundred.
After you've taken care of those see the boys at Red.Dot and get them to do a custom remap on your TS for you. Apparently you can choose where in the rev range the power has more effect on.
If you are using it for track use I recommend having more mid-range speed thrown on, as once after take off you won't be stopping all that much anyway. And depending on the types of track you plan on taking on you might want to get a mid-high speed remap done.
They cost about £200 but add about an extra 15-20BHP usually.
The weight of the TS engine makes them an ideal track car as their handling is so much better than the V6. (I had one)
Do you have a Sport Pack Alfa? (Black speedo dials) or Standard? (White dials) The SP's came with 16" wheels and side skirts as well.
The current suspension set up on SP's (Sport Packs) is adeqaute but if you have a standard car then you'll want to change the suspension fairly soonish.
Same goes for the brakes, whatever 156 you have if you want to track day it you'll definitely need upgraded pads and discs. Green Stuff track pads are supposedly great so go with them all round. The discs on the Alfa are supposed to be pretty good but change them w/ some grooved / drilled jobbies. Any major make will do.
This lot will probably set you back around a grand in total but to be honest it's an idea I'm tinkering with myself. Just for road use though,
Are you stripping the car as well or leaving it?