In terms of data logging, you just need NIStune and the consult cable. The consult cables I have always used are these:
The good thing about them is they are directly USB compliant, whereas many other cables use an RS232 link which then needs to be converted to a USB output for easy plugging into a laptop (not too many modern laptops still have RS232 ports!). I've never had one fail and the drivers are easy to install. But feel free to go down any route that offers a cheap solution. I think most modern-day consult cables should be fine, just remember to buy an RS232-USB adapter if you need one.
If you want to physically make changes to the ECU, then you'll need to splash out on a NIStune daughterboard (which needs soldered into the main GTiR ECU) and a NIStune licence. A single-user licence is good for tuning as many GTiRs as you like, but you'll not be able to tune other Nissans should you move on to new pastures. The good thing about the single-user licence is it's a LOT cheaper than the tuner's licence..................... Sometimes you see GTiR ECUs that already have a NIStune board installed come up for sale (either here or on eBay), and these would be your cheapest way of getting a ready-to-map NIStune ECU. Failing that, I get discount on NIStune boards, cables, and licences direct from NIStune so if you decide to go down that route give me a shout first and I'll see how much discount I can get you.
The NIStune forums are a very good way of learning how to tune safely and efficiently.
Let me know if you need any help.