Martin, I can't speak for everyone, and my self-taught Theremin experience is different than most, but I believe if anyone devotes themselves for an hour or more a day to literally any instrument they'll be good at it in a year - "good" depending on your expectations of course. Having a good instrument IMO is vital to keeping your interest up. You already have a musical background so it should be easier for you. It seems folks who come from cello (Theremin himself), violin (Clara Rockmore), or musical saw (Gregoire Blanc, hYrtis) take to it more naturally, which is understandable. I played trumpet as a tween and guitar since forever, and Theremin has felt fairly natural, maybe because I'm a lay singer too - maybe it's because I built the thing! But I'm a jack of a few trades and master of none, so my views should be considered suspect. Consider (do as I say, not as I do!) getting a few video lessons from a good player, like Randy George or Carolina Eyck. I think there are free group classes here and there too. There are many fingering techniques out there to choose from, maybe pick one that seems less likely to cause you further injury.