AFAIK it was only the 3 litre facelift that needed a 17" to clear the front brakes. I had a 125/80 x 17 for my previous Coupe which is what 330i and 330d E46s had, also for front brake clearance.
The rest of the E46 range had a 125/90 x 16 which is what you probably need as the E46 and E85/6 shared several wheel sizes and offsets (both were sold with MV2s for example). But if your front brakes have been upgraded you'll need something bigger.
I got an E46 jack from a breaker as it fits the Z4 jacking points but you'll obviously need a wheel-brace too. And don't forget if you ever use the space-saver you'll need to get a full-size wheel in the boot!
Because a space-saver is only good for 50mph and a limited distance (200 miles or so?) I carry a full-size wheel in my car for trips like last week in the Scottish Highlands 600+ miles from home.