I, too, have very limited space, and need to set up the theremin each time it is used. This certainly makes it harder to grab a spare ten or fifteen minutes of practice time. Those wires, the amp and the microphone stand can, at times, seem a lot of bother, and I imagine that with your circumstance they are possibly a greater problem.
I think your idea of playing along with some music is perhaps a good one at this stage. It's great you are having fun, and I think it's wise to keep it that way. I know that in the early stages, before settling down to learn any pieces right through properly, I would simply play along with favourite tunes, working my way through CDs or my iPod, not necessarily repeating or practicing pieces over and over, but keeping it fresh and fun by trying a piece I liked and then moving on to the next one. I'm not sure whether this is somthing generally advised, but I felt it worked well for me - even though it might seem undisciplined, I think it helped to train my ear; I think it's easier to drift out of tune without realising when playing unaccompanied, whilst playing along with music helps you to keep making needed corrections. I also found that it was much, much easier to play something I knew really very well indeed; often something firmly entrenched in the brain, like songs sung years ago at school, or, in my case, melodies I'd either sung or played on another instrument and felt thoroughly familiar with.
The important thing is enjoying the process ... which you sound as if you are doing!
I think your idea of playing along with some music is perhaps a good one at this stage. It's great you are having fun, and I think it's wise to keep it that way. I know that in the early stages, before settling down to learn any pieces right through properly, I would simply play along with favourite tunes, working my way through CDs or my iPod, not necessarily repeating or practicing pieces over and over, but keeping it fresh and fun by trying a piece I liked and then moving on to the next one. I'm not sure whether this is somthing generally advised, but I felt it worked well for me - even though it might seem undisciplined, I think it helped to train my ear; I think it's easier to drift out of tune without realising when playing unaccompanied, whilst playing along with music helps you to keep making needed corrections. I also found that it was much, much easier to play something I knew really very well indeed; often something firmly entrenched in the brain, like songs sung years ago at school, or, in my case, melodies I'd either sung or played on another instrument and felt thoroughly familiar with.
The important thing is enjoying the process ... which you sound as if you are doing!