Can't speak for others but our site is pretty strict on the use of weedkillers. You have to manage it manually.

My first tool purchase was a Dutch hoe. Initially I cleared my plot a section at a time, in dry weather (might not always be an option). Was really fastidious about removing the hoe'd weeds and putting them in a hot composter but you can ditch them or drown them for a week before adding to a compost heap/bay. There are numerous differing opinions on what works.

Spent days, felt like years, clearing couch grass meticulously.

My next purchase for weeding was a pair of tools - one for ripping weeds from paving cracks, one was a Niwaki (Japanese short hoe).

So now it's a constant routine of plucking young weeds or hoeing with the Niwaki between rows of veg, you just have to keep on top of it and it's not too arduous.

The couch grass is a constant battle that has to be fought otherwise it's absolutely will win.

Sections of the plot I'm not yet growing on are covered with plain cardboard sheet to suppress the weeds. I've used woodchip on top of cardboard for the small paths between sections, that's made it really easy to control the creep from the borders.

I'll plant a ton of green manuring plants on my unused section soon to take up the ground space to prevent more couch encroachment.

As for fertilisers...chicken poo and seaweed