@ kero .... Playing piano gets far more involved than how many keys _ if you are making a serious, long-term effort. You can learn many important aspects on lesser number of keys. Much depends on how you choose to go about this and how committed you are.
Much has to do with muscle memory, and all its complex factors. This comes from learning many different techniques by repetitive, error-free practice ... and does not require 88-keys, initially.
Chord progression is a vast skill in itself and not dependent on number of keys.
Key touch is very important (AT SOME POINT). You are talking $700. (used) to $1,000. ++ for Roland A-88, Roland RD-300NX, NI S-88 to get keybeds comparable to quality acoustic pianos. Top pianists/keyboardists can still do magic on lesser keybeds.
Listen to Jordan Rudess playing on almost anything !
Not a specific answer, but lots more to focus on early than 49, 61, or 88, IMHO.