Learning piano is fairly valuable in terms of understanding/writing music, but not critical.
If you're interested in making music with synths, you could probably get away with a pad controller. You lose some keys, but you usually get a lot of control buttons. A 16 button pad controller can do a lot when configured with 4 banks of sounds, with root/3/5/7 of each. Most controllers have octave up/down buttons, so 4 pitches of a given sound is actually very versatile.
If you're interested in making music with synths, you could probably get away with a pad controller. You lose some keys, but you usually get a lot of control buttons. A 16 button pad controller can do a lot when configured with 4 banks of sounds, with root/3/5/7 of each. Most controllers have octave up/down buttons, so 4 pitches of a given sound is actually very versatile.