Have a look at these sites to start with, and you may find the answers to some of your questions

Tire size calculator

http://www.1010tires.com/TireSizeCalculator.asp 


Wheel offset calculator

http://www.1010tires.com/WheelOffsetCalculator.asp 


Will they fit

http://www.willtheyfit.com/ 

thankyou helbus!!!!!!!!!! seems to confuse alot of people

cant remember the other one thats good but it was some american mx5/miata forum thing i think

Thanks man .. this really helps!

Have a chat to John Sherman from Volskconversion on the coast , he some decent looking 15 inch wheels with 4x130 stud pattern or can give you hand converting your stud pattern into any one you like (I'm thinking of doing that and upgrading mine to disc at the back.

I have been looking at the wheel adapters https://www.classicveedub.com.au/cvd_new/part_detail.aspx?parts_id=18199 
will these go onto a wide 5 drum so that a narrow 5 stud pattern can then fit on?
I am wanting to go to discs so would it just be easier to buy blank rotors and have them drilled out to match the rims I have?

just be aware that adaptors like spacers are illegal unless engineered.

This can help as well.

https://www.wheel-size.com/size/volkswagen/