Space saver for E90

Im currently looking to buy a space saver for my E90 seeing that ze-Germans thought it would be a good idea to bring out the car without a spare wheel

I will be going the non RFT route in the future, so getting a space saver is the logical choice from a safety point of view.

Im planning on getting a 2nd hand one from a scrap yard or on the GUM, and purchasing a jack & wheel-spanner from the local hardware shop. Im planning to get some sort of nylon bag, and securing the wheel in the boot (I saw a pic on another thread, cant find it now tho)


A few questions;

1. Considering I currently have 16inch rims with 205/55/16 tires on my car, what size space saver should I be looking for? From my research I found a 17inch for the E90, with either a 135/80/17 or a 125/80/17 tire. Would this work with my car, or must I get a 16 inch?

2. As long as the Rim is 5/120 pcd, should I worry about anything else, offsets? ect?

3. How would one examine and choose a 2nd hand rim & tire? By that I mean what are the things to look for and avoid? I dont want to end up with a buckled rim, or anything similar...