Hey James! Welcome to the posting side of things here at THP.
Cooking after fermentation is not necessary at all but I cook anything I am going to bottle in order to stop fermentation. You don't want to bottle a ferment that's still active because it can explode - continued off gassing with a closed/sealed hot sauce bottle will end up gushing out all over the place when its finally opened.
Regarding individual ferments for the purpose of later blending - that's fine. Not every ingredient ferments very well on it own though, so perhaps something to keep in mind. It's like both sides of the equation; 5lbs of peppers can be fermented on their own and blended with other ferments or you could do 5 batches of 1lb each with varying levels of ingredients. Sometimes the journey is just as important as the destination - all I'd ask is that you photograph/document such an experiment here for all to see.