If you want to use a guaranteed poultry-friendly detergent, get some Poultry Shield and use either as a spray, or diluted for cleaning surfaces. The best disinfectant cleaner is Barrier V1, which can also be used in kitchens, it's used in restaurants etc as an organic disinfectant with a pleasant herbal odour. Expensive to buy, but used as directed, highly diluted, it's longlasting. Or you can just use whatever you have as a kitchen cleaner - once you've rinsed off the dirt+detergent from a smooth plastic surface it's unlikely that any harmful residue will be left, and if it's OK for your family it's OK for the hens!
I don't feel jet washing of your plastic coop will be necessary if you poo pick it regularly. Just put in a nice layer of Aubiose or whatever you're using as bedding so the floor is well covered, then poo picking will leave the surfaces clean underneath. A plastic coop is reassuringly heavy which means that you don't want to be moving it around out of the run, and jet washing will make a very wet area, scare the chickens, waste a lot of water, and also it'll take ages to dismantle and put back together again. Just keep the coop reasonably clean with a daily poo pick, and wash down with a bucket of hot water now and then when you notice dust is collecting or the surfaces are stained with poo. I find that poo stains wash off easily with a cloth, hot water and disinfectant. You're much less likely to get a redmite infestation in a plastic coop, and unless and until you do, there's no need to keep taking it to bits. As you say, 'less is more'!
I agree about the way businesses queue up to sell stuff to new keepers, lots of it totally unnecessary! Healthy young pullets do not need any supplements. Do not bother with Vermex, for example - not effective as a wormer and not necessary. They do need a course of Flubenvet wormer when they have settled down in their new home and are all eating well, to deal with the worms they will have brought with them, having been reared in premises which have a lot of other chickens from various sources. It's also worth getting some purple disinfectant spray and some antibiotic powder for your poultry first aid kit, in case you ever have to deal with chicken injuries. You probably won't ever need these, but if you do, you'll need them immediately. You'll need a dustbin, preferably metal, for layers pellets; a plastic bucket and gardening gloves for poo picking; a dedicated washing up brush kept by the tap for cleaning drinkers between refills; some bricks or a concrete block to raise the drinker to chicken chest height to reduce mess being scratched into it; at least one feeder and drinker, spares are good; a large plastic container at least 40 cms deep, with 10-20 cms of play sand or dry earth in it for their dust bath, in a covered dry place; and if possible, long wooden perches about 40-50 cms off the ground, looking out of the run for them to sit on and enjoy the view. If you have Leghorns or other flighty leghorn-hybrid breeds they'll like a high perch as well - my last flock were all told to roost up there every night by the top hen, who was a leghorn, and the coop stayed lovely and clean inside for months on end!