If you get just the nailer you should be fine. Just avoid anything "2 in 1."
To me, compressors should either be huge or tiny. I like the $99 porter cable pancake compressors as they are easy to move around the house. I also have a 20 gallon that barely gets used. It's overkill for a nailer and too small for any other tool I own/want. But, that's just me. Get whatever suits your needs, just don't expect a 10g to run an air sander, etc.
If the compressor is just going to sit in one place though, might as well go as big as you can.