What Clayton said. Ideally you want fuel control and a whole host of other things but you can do well by putting a larger turbo on before the supporting mods if you keep the boost down. Don't expect huge gains from a bigger turbo with no supporting mods and resist the urge to up the boost but if you need a turbo it makes more sense to upgrade now then buy stock and buy again later.
Also converting to a 14b style turbo will help out because you can swap in any 16g or other similar bolt-in turbos on a 1G. 14b, small 16g, big 16g and evo3 16g are all the same externally and if you get the oil line and j pipe and whatever else for your 2G any of those will be a bolt in.
Look into Charn's setup, it's got all the 2G conversion parts plus a big 16g is a good upgrade turbo.