The Mégane II Owners' Club

Ok, after some advise. I been looking for some wheels, found a few that i like, but after reading some other threads, im really confused about size, offset, and tyres. Im looking at either 17" or 18" wheels, and lower it a few mil later on. So what the ideal sizes? I dont wanna get some 17s for them to look tiny, but at the same time, does the wheel size affect the speedo?

Thanks
Matt