I was in a same boat not that long ago.
And I went for 61 keys and never regret it since.
Yes it takes some serious space(I have Novation Sl MK2 61) and needs a stand but it really makes a difference cuz I am not touching octave shift buttons that much and can play with both hands without any problems.
You will quickly learn basic triad chords, it is not a rocket science.
But for more advanced chord voicings stuff more keys will be more convenient.
I am learning jazz stuff now and improvization with both hands takes whole keyboard sometimes. So my vote goes for at least 49 keys if you want to actually play keys.
But if you are going to play only with one hand to, for example, sketch chords or for very basic stuff, 25-32 keys will be enough.