Remember to look at the fuel pressure regulator and the fuel pump as well, if you go to a larger turbo.
On the Sport300 Lotus used a larger turbo, another ecu, a better pump in the right hand tank and a modified fuel pressure regulator. They kept the chargecooler standard, apart from a 10mm cut off on the inlet side, to adapt the larger turbo.
On a secondary note, the following may be of interest to you, if you upgrade the turbo:
An adjustable fpr may be the way to go for you. Also, at that point you may want a better exhaust manifold, say an alunox one, which flows very well. They are at their 3'rd generation, so they do optimise over time. This flows far better and can follow any upgrade you may do, now or later. Then comes the cat, which should at least be investigated for flow, as they get old and bits fall off and restrict the exhaust, which may have consequences. I used a slightly larger more free flowing cat and it's stil street legal and cleans the exhaust gas and pass inspection.
In connection to this, you may want to look at the mechanical chargecoolerpump, which could be changed for a more reliable electrical one. Lot's of threads with a discussion on that topic.
At that time you do want to install better brakes, if not already
Some good Guys over in the UK developed a kit to remove the abs system, as the old one installed seems to develop some problems over the years, for example because of not changeing brake fluid every year or every second year. The later abs system as on the 2 Liter GT3 had a more modern faster better reacting system.
You may of course, have done all of the above already.
Let's hear what you decide on and to what effect.