Don't you worry too much about them, they look great, peppers usually are strong and persistent.
I think letting them flower is a good idea if you don't want to repot them into bigger containers, if you want to give them more root space, flowering can slow it down. I am curious how people here care for their peppers sown in october/november. It is my first season, so, I am experimenting. I have few of them ready to be repotted but I don't have place for 5 galon containers in my apartment, so, they will stay in small ones 'till warmer months. Until then I will let them flower and fruit.
In case of fertilizers, I can't say I know what to use other than those made from kitchen scraps for nitrogen and phosphorus, banana peals for potassium. Nitrogen for vegetative growth (I like to make some nettle slurry (I hope that is a good word in english) in bottle), phosphorus for roots, flowers and fruits, potassium (banana peals in water) for overall health and some science stuff. Warning 1: It's smelly. Warning 2: can't be used without watering down a lot.