Lets be fair, an R5 T2 turbo is old hat now, so too the T3. They do their job but there are plenty of much more modern turbos out there which are far better. Zero back pressure down stream of the turbo is ideal but hard to acheive especially in a road car so a decent flowing turbo-back system is a good start. The elbow coming off the turbo can be fairly restrictive in most cars so this is worth looking at too.
For safer higher boost levels, the C/R can be easily dropped with out the use of fancy forged piston. It will just require 2 head gaskets and a steel spacer laser cut to the same shape. This will make the engine slightly less responsive but with some clever ignition mapping, hardly noticable.
That brings us to the software which is by far the most important thing about turbocharged engine. There's no point fitting a bigger turbo, more efficient I/c and tons more boost if it can't be safely controled. If I were in you shoes now, this would be the first thing I'd invest in. Emerald, DTA, Polestar, Motec.....there's loads out there. They all vary massivley in price too but that only depends on what you want from them. If you feel brave get a Megasquirt. They are cheap as chips, do a pretty good job at what you tell them but you just have to be handy with a soldering iron lol......
......and I know you probably know but don't forget to upgrade the running gear accordingly lol