Hi 

I am new to this group. 
 

I want to buy a set of wheels and wanted to know if anybody has any advice on how the offset and width would sit 

I’d really appreciate it 

This link gives your standard offset etc

https://www.wheel-size.com/size/subaru/wrx-sti/2015/

This will tell you what impact the new wheels will have, increased / decreased clearance etc

https://www.1010tires.com/Tools/Wheel-Offset-Calculator

In this case going from a 55 to a 35 offset means your wheel will stick out an extra 14mm from standard