Fitting suspension and bushes is an expensive job, the parts alone will set you back about £600 and if you have the work done in a garage labour will cost you another £300 or so. You could fit everything yourself to save money but some of the bushes are a nightmare to fit. Its a worthwhile job though because when its done the car will handle like its new.
T3 should be good for 22 psi, power will depend on the condition of your engine, parts used and the mapping parameters built into the chip. You say your engine isn't a smoker but as its only boosting to 13 psi and dropping off to 11 its probably only running near standard power and not really under any stress at the mo. When you up the power any internal weakness will show up pretty quickly. Reputable tuners would discuss all your options before carrying out any work and they are the best ones to advise you, but if at some stage you plan to up the power further by fitting a T34 then it would be wise to fit a proper breather kit a stronger headgasket and an uprated clutch