First off welcome
As for info on the 40th anniv. model (I've got one myself) apart from the pillar badging, the seat badging and some extra available factory options, they're the same as any other S2 R33 albeit built in 1998 just before the R34's (or very late 97 for some).
As far as mods go, best place to start is always with the exhaust (power wise at least). You already have the cat back, so the next step would be a 3" dump/front pipe and a high flow cat which would complete the exhaust system and give you a nice gain in power.
From there depending on what path you want to take (or take first) you can go with an upgraded intercooler (R34 side mount if you don't plan to go much past 200rwkw, which the stock turbo will do) or a front mount if you plan to go further with an upgraded turbo etc...
There's plenty of mods to get good power, but don't neglect suspension, tires and brakes.
Have a good read through the various sections of the forum, and utilise the search function to find all the info you could ever want on your car and the different ways to go about modifying it
Congratulations on the purchase