Hello,
Somehow I managed to finish this, with no real idea of exactly what the theme was :) ... but I have spent a long time on it! In the end I quite enjoyed it, even if I found some clues almost impossible to parse!
Some much easier, but I found myself massively overthinking some of the easier ones, assuming they were elaborate wordplays too!
I also had no idea how to parse 12a - I just put the obvious answer in based on crossers and the first word being the definition.