Ok, so it would seem the day I make a lenghty post asking for help, I find a fix.
I must have made my millionth google/forum trawl, and came across a RDR2 forum where someone had a similar issue. Somebody mentioned to try "EasyHookPatch". I've nevr played any Red Dead games, but I know they use the RAGE engine. I downloaded the zip and plopped a small .asi script in and voila!
Ive started my highly modified Tuners SP, my slightly modded Contract SP and tried a clean install with LSPDFR, hasnt crashed once. I've opened a lot of browser tabs, played music and had programs open as well.
Log for any curious people:
The issue I had still exists but it's able to move past it:
JessicaAltezza's post in Crash "Exception message: STATUS_NO_MEMORY: Failed to allocate memory" was marked as the answer