For use in a home studio.... 61 keys is often plenty. Since you said you were amazed by those who can use both hands at the same time to play.... yeah... 61 is plenty.

I have 2 keyboards. Both are 61 keys. The good one is a Yamaha DX27S which was state of the art when it was bought. I picked it up second hand from the keyboard player in our band. Long story on that... for another day.

The main thing is do you want something that plays and feels like a piano? If so, get something with weighted keys. To use it for any other purpose, unweighted is good. Both of mine are unweighted and the cheap one is actually touch sensitive but unweighted. When it comes to using a DAW and soft synths like Kontakt or something else.... midi is midi and any keyboard that has midi out will get the job done. I don't think I have ever recorded with either where I used the audio output. I have always just used them for their midi. Reason being..... I can easily edit the mistakes. Two hands only means twice the number of mistakes in the same amount of time....at least for me.

You can find my music at:
www.herbhartley.com
Add nothing that adds nothing to the music.
You can make excuses or you can make progress but not both.

The magic you are looking for is in the work you are avoiding.