i have a question
 

if i was gonna get new rims for my z say 18 x 8.5 in the front 18 x 9.5 in the rear what would i need to pay for besides rims and tires

-mounting
-balancing
-alignment
and also what size tires in the front and rear?

As for tires, I just put on 245/45-18 on the front and 275/40-18 on the rear on the stock 18" wheels. These tires will also fit on the rims you want to buy. Unless you are having alignment problems to begin with you shouldn't need an alignment. Mounting and balancing can range from free to $30/tire or maybe more from my experience.

what about the tpms what do i do with that the new rims come with it and i have to get it set with nissan

Like IDZRVIT mentioned, I did the same thing and just replaced the stock wheels and kept the 245/45/18 on the front wheel and 275/40/18 on the back wheel.

As far as the TPMS, I just used the ones that came with the new wheels and discarded the old ones (for whatever reason, I was told that the old ones couldn't be used).

Most of the time you can usually swap the factory ones to the new wheels. Some people purchase new ones, but they are a little pricey at times. We mount and balance wheels and tires for free and can set up an entire package for you, but depends on what you are looking for. Feel free to contact us and maybe we can help, if you have any random questions, feel free to ask, you dont have to buy from us to ask a question.