A 6 is a bit small for C band. It'll work, just not that well. Won't get many of the new generation S2 signals. Number depends on many factors. (Many have experimented with dishes as small as 1 meter(36 inch). 7.5 ft and up are recommended. 10 ft being the 'norm'.
For Ku an excellent starter package is offered by Satellite AV. (site sponsor) http://www.satelliteav.com/p/shop/?ws_pid=1611&ws_cat=413 (up to a 1 meter dish is protected by OTARD)
Receivers do not determine which band, (C or Ku) you receive, the LNBF will determine that.
Depending on your location if all you can put up is a 6 footer I say go for it. I have a 6 footer and really I'm quite shocked at it's performance! Now it wasn't easy getting it tuned but I just took my time and kept at it. The only real problems I have is from 91w-99w where the sats are closest together at my location and I get some interference from other satellites. I still pick up the channels it's just sometimes I get channels from other birds. I just go into the channel editor and delete them. Everyone told me it would be too small and I'd be disappointed so I went in knowing that because I can not put up a bigger dish period wether I want to or not. Really I'm VERY HAPPY with its performance! Would I like a 10 or 12? Heck yes, but its not an option! Just saying if a 6footer is your only option with some persistence it will work and quite well!
oh i know id need a 10 or 12 for c band but id rather not push my luck with the land lord, im limited to a 6ft or smaller, i was thinking ka ku signals any way and possibly some c band signals, more less doing it just to experiment, as i am a radio hobbiest and that is get to expensive. thinking about trading my radio gear for fta stuff.
I say put up a KU dish get a receiver and dabble in it a little. Getting KU set up is VERY inexpensive even motorized. If you enjoy it EXPAND. I can tell you I don't find myself on KU band very often, I'd say 85% of the time I'm on C-Band.
i have both 7.5 and 6 foot dishes. yes, the bigger dish will get quite a few more c-band channels including ewtn on 133w which so far i haven't been able to get with the 6'. with a dual band lnb the six foot dish is acceptable if you can't go any bigger.