Okay, panic mode is over, and I've just about worked out the kinks in my screenplay.
I've laid out most of the main plot and a lot of the subplot, and I do believe I've got it all straightened out. It all started from figuring out what was really the subplot and what was just a plot layer of the main plot.
So I realized that anything depended on the main character's story was just a plot layer. Anything that was independent, that branched off and did its own thing, connecting and intersecting at certain spots until maybe at the very end, was indeed a subplot. The subplot contains its very own main characters.
That let me see that I had 5 plot layers (for each supporting character that had a small arc and resolution that related to the main plot) and 2 subplots (for the characters that had their own branching stories). I lopped off one subplot, and voila-- I had simplified my story to a manageable level.