I agree with Erci and Xavias. Gear first, then bike maintenance, then mods. Since you don't know what the previous owner did as far as maintenance, I would start by taking care of these basic maintenance items:
1. Check chain slack, adjust if necessary. Clean and lube chain.
2. Replace and bleed front and rear brake fluid
3. Flush coolant system and replace with fresh coolant
4. Change oil and filter (I use Rotella T6 5W-40 and a Purolator PL14610 filter).
5. Check tire pressure (36/39 F/R is what I ride with).
6. Check steering head tightness (Put bike on center stand, weight the back end, and see if there is any play in the forks).
7. Change spark plugs (NGK CR9EIK or CR9EK).
8. Change air filter (if bike has more than 15K miles on it).
9. Lube clutch and throttle cables (I use the same T6 oil).
10. Check brake pad wear front and rear.
Most likely, a lot of those maintenance items are not necessary for you to do right off the bat, except for # 1, 4 and 5.
If you do all of those things, you will have a bike that runs as good as new and won't give you problems for a long time.
Next, Mods :rockon:
I have done: Puig light smoke windscreen, frame sliders, Rizoma signals front and rear, FZ1 handlebar, custom heavy bar ends, new handlebar grips, fender eliminator, BD43 dual headlight mod, SAE plug for heated gloves and heated grips, All Balls steering head bearings, 17T front sprocket, EBC brake pads F/R. I think that's it. The signals, frame sliders, and FZ1 bar have been my favorite mods. The sliders have saved me countless amounts of money in standstill drops both by me and my girlfriend.
Anyway, good luck and remember, gear before any of my preceding post.
How many miles on the bike?