Lighter wheels (smaller) are better for handling.
(This is because lighter wheels have less unsprung weight, this means that while the wheels are riding over the road every little imperfection (bump) will cause the wheel to jump upwards to the top of the car, it is the suspensions JOB to keep the wheel on the ground. Now if the wheel is heavier than when the wheel bounces of a bump it will have more momentum than a lighter wheel therefore will be in the air more and not on the road where it should be. So obviously the lighter the wheel the easier the suspension can push the wheel back down.)
However larger wheels means you have space for bigger brakes. So on a pure drivers mind, you have to decide whether you can make more time from larger brakes or better handling.
This is why rally cars have large wheels because they can brake harder and save more time instead of having small tyres that handle well but will have small brakes.
Width of wheels is more difficult, to narrow and you will have less tyre on the road to grip with, too much and you will have too much unsprung weight making your car handle worse (your tyres can be as wide as 40inches but if they spend most of their time in the air then whats the point)
This is why F1 cars have narrow front tyres because they need max unsprung weight on the front for grip and wider wheels at back to get traction for all the power they have.
Brakes
Another common idiot belief is that if you mod your car to go faster than you should get bigger brakes. If you think about it, no matter whether you have 800HP or 80HP if you are going 30mph in the same car and only the HP has changed than the brakes will still be as effective as they were before. But if you ae modding for more power you hopefully would have learned by now that bigger brakes means better track times.
Spoilers
Spoilers make your go slower but do increase downforce and grip at high speeds.