hi I was wondering if most of the sheets posted here can be played with a keyboard (61 keys)? aren't we "limited"?

88 keys is standard. Stay away from 61 keys because it lacks a lot of bass which you will definitely need. Transposing it 1 octave down doesn't help since you'll lose the highs as well. If you can't get 88 keys, then get one with 76 keys. Action-graded helps too.

I learned to play with 61 keys for a fair amount of time. A lot of songs can be played in that space but those songs are either really basic or lack expression IMO. All of the really good songs have a large mixture of both low and high notes. But if you're just beginning, don't worry about it... especially if you're low on cash.

If you can you should try to get an 88 key. Everyone says its "ok" for beginners but if your really gonna learn, learn it the right way with the full keys. The best time to learn is when you start right off and if you can, learn from a real piano. That way, you know how the pedal and keys feel and differ from digital ones. A keyboard will be alot easier to play, especially with a few or no lvls of sustain you dont need as much combined concentration and focus.