I'm new to this whole upgrade business, I'm getting pretty confused about the right fitment for wheels and tires.

I've decided on
AvonTech M550 a/s 225/40/18 tires
and
Motegi FF7 glossy black 18/7.5 wheels.

Can anyone tell me for sure if these are compatible, and if they'll fit the car without problems? I read about offset being important and what it is, but I still really don't understand it (or most anything else) enough to go buying this package.
I'm planning on getting the prokit installed at the same time, if that makes any difference.

Sorry if this is a question, but after reading all day, all I know now is that I don't know enough to make a decision like this yet.


Many thanks