Self-funding few OU modules - access SF later for regular degree?

I want to attend Uni to get a STEM degree (plural), however that's not possible right now due to circumstances, a delay of a year or two.

In the meantime, I want to self-fund part time study of an OU module here or there, for personal interest, maybe a philosophy module here and a history module there, the world's your oyster.

Would they fall under the previous study rule, even if they're disjointed modules here and there, and if so how much funding would I lose, and under what circumstances? Is there any policy or guidance I can read for further details?

I've read that there are exceptions for STEM degrees as well, if all fails, how does that work?

I do not wish to take a break from academia, but I cannot afford to jeopadise SF funding for the four-year STEM degree I want to take in the future.