Leah,
The theremin is unlike traditional instruments in that there is no established method of playing it. If you wanted to learn the cello or the concert harp, just about anyone who has been playing for a year or two could show you the basics. Not so with the theremin. Most thereminists are self-taught and no two play alike.
One of the problems this has created is that with no competent teacher to oversee their progress, many budding newbies have unwittingly developed habits that later interfere with their ability to advance. This can be very discouraging and is one of the reasons why the dropout rate is so high among thereminists. While there is no "right" way or "wrong" way to play, there are approaches that will help you get where you want to go and others that will hinder you.
You say you have an "ambitious project" ahead, so you already seem to have very specific ideas about where you want to go and what you want to do with the theremin. This is good. The great theremin virtuoso, Clara Rockmore, once said, "The most important thing for any newcomer to the theremin is to know, before starting out, exactly where he or she wants to end up."
Do you have a theremin? If so, what sort of theremin is it? Do you play another instrument? What sort of music do you want to play? If you are into the avant garde or experimental genres (as opposed to more traditional kinds of music) this could have a bearing on the kind of theremin you should play and how you should approach it from the point of view of technique. Is it by any chance your intention to compose for the instrument?
CARDINAL RULE: Never take any advice on how to play the theremin from anyone whose theremin playing you have not heard or do not enjoy. Theremin playing is like religion - EVERYBODY IS RIGHT - including those who fundamentally disagree with one another! LOL