Welcome aboard.
Plenty of options available on tyres & exhausts but plenty of answers have already been given on the forum so try a little search (usually better searching google & just adding "350Z UK" before any queries).
The best tyres though considered by most for the Zeds are the Michelin Pilot Super Sports (MPSS), ...for a lower budget option I'd recommend the Falken 453's.
The exhaust though is such a personal thing and really does depend on your budget & the look you're after. Also your car might be too loud for you at the moment as it may have HFC's (High Flow Cats) or De-Cats although if it's as loud as you say it is then it's probably the latter.
Take some pictures of it underneath when you can and maybe some of us will be able to identify which you have.