Well, I count 4 questions rather than two.
And you need to clarify what you mean by "electric organ". That label can be applied to organs with a motor for air supply (but that's basically every church or theatre or other pipe organ these days), or it can be applied to tonewheel organs (of the Hammond persuasion). But the former does not readily fit in living quarters (assuming you aren't Count Dracula in which case we are more talking about undead quarters anyway), and the latter does not play an "amount of instruments". And will still provide the challenge of finding enough room (if we are talking about a nice classic like the B3).
So you are likely either talking about some electronic organ with analog circuits, or some digital organ with sampled sounds.
Now the problem with sampled sounds is that people don't buy into mismatched visuals. If your controller looks like an accordion, they expect to hear an accordion. If your controller looks like a piano, they expect to hear a piano. If it looks like an organ, they expect to hear an organ.
As a male alto, this was pretty annoying to me until I got tired of people's unflexibility and gave them suitable visuals when performing.
If you are doing studio recordings, you don't need to bother with people's expectations (Frank Farian is a notable producer who put up various show/playback bands for stuff he had been singing himself: great and flexible voice but looks like an accountant).
So if you are indeed talking "amount of instruments" rather than "sampled organ sounds only", you are more talking about a generic "keyboard controller" than an organ, something that's nicer for producing rather than performing. They start from a dime a dozen (though if you want to emulate organ, you'll have to invest into pedals as well).
The main question you need to ask yourself is why you want to play an "amount of instruments". Any digital instrument will usually be less under the control of its player than the original it is copying because it has only been sampled with a finite number of use cases. For producing music, 50 pretty good sampled instruments are definitely useful. In a band context, being able to play 2 actual instruments for real is usually valued more.
If we are putting the "amount of instruments" thing aside and really just go for organ, the main challenge is the difference in articulation. An organ does not really mind how hard you strike the keys but it is very much more particular about when you let go of a key. Because that does not just apply a dampener on an already decaying note but cuts the note off from full to nothing. So legato play and fingerings are a completely different issue from what you do on the piano.
Also if you are playing actual organ music, you'll need to work the pedals. That's another challenge quite outside of the piano experience.