you're right about the ratios and nutrients interacting, but I think in practice it's much less of a problem as it seems. yes there are some slight differences in needs between different plantspecies, but for my gardening I still grow lots of different kinds of veggies in the same pot, and they all get what they need, no defficiency and no lockouts, the differences in needs are so small that I mostly just treat them all the same(some slight differences though, like I will never throw lime into the pot that houses my blueberry bush). also helps a lot if you're not trying to feed as much as possible, but just enough to not get any defficiencies.
my biggest issue with those recipes is that they use lots of ingredients, and they contain a lot of hard to find ingredients, and there's a big overlap in ingredients, like multiple ingredients that mostly supply the same nutrient(I can imagine the purpose is to make it release over a longer time with ingredients that differ in breakdown rates, but you could just simplify it by choosing 1 ingredient per nutrient, and topdress some later to get a similar effect). it also depends a lot on where you live, but I get the idea a lot of those soil recipes I read online are thought up by someone in the US, since they often contain some ingredients that are nearly impossible to find around here(like I've been searching for gypsym for a while so I could experiment with it, but no luck. recently I did accidently stumble upon it, turns out some mushroomgrowing webshops sell it to mix into the casing layer. but other than that, I haven't found any site that sells gypsym to regular consumers, only sites that sell to companies/farmers).
things like alfalfa meal, kelp meal or worm castings are also products you won't just easily find in a physical store around here, but have to hunt for online and have it shipped to your house.
if instead to sticking to such a recipe strictly, but just use it as a starting point and look into what each ingredient's purpose is, and understand why the recipe is what it is, you can adapt it to what you are able to get locally, which could save you a lot of trouble hunting for all those hard to find ingredients.
ofcourse it depends on what you personally like, but I like to understand what I'm doing as much as possible, and I hate strictly following recipes or instructions, especially if it's not clear why I'm doing something. so my advice is based on what I would like to hear if I was asking for advice.
my love for chicken shit comes from the fact it's just 1 ingredient that takes care of pretty much everything a weedplant needs(with the only caveat it has too much N for flower), and it's easily and cheaply available anywhere in gardening centers, no need to order it online.
I actually got the idea of chickenshit from a recipe, when I started growing I started reading around on a dutch forum and there was an older grower there(passed away by now, unfortunatly, his user name was 'dame blanche'), like me he was from the north of the country, so the way he spoke fitted well with me. like a sober farmer, keeping it simple and using common sense(he also had a nice story about how some guys took regular clay soil, dried it and sold it as a micro nutrient garden ammendment with a lot of profit).
so this guys recipe was(meant for holes in the ground):
-1/3 local soil
-1/3 fresh potting soil
-1/3 used potting soil (he went around asking indoorgrowers he knew for their used soil)
-1 cup of chicken manure per 10 litres of soil
he then recommended to apply some generic synthetic fertilizer pellets around the start of flower, to take care of nutrientneeds during flower. I think he said a handfull or so at the base of each plant. I never did that, but I have seen why he'd recommend it, during flower the chickenshit starts running out, and I've seen some symptoms I suspect were K-defficiency. so for ideal results you need to add some fertilizer that's not too high in N around that time.
I think he used a slightly different recipe himself(this recipe doesn't use worm castings for example, but I know he did use those), but this was the recipe he recommended for anyone starting out, since it's simple and it works.
myself I don't know any indoor growers irl(or well, any growers at all, only 1 former housemate who used to grow guerilla), so in my pots I've just kept the 'cup of chickenshit per 10 litres' part, and ignore the rest of the recipe. and since it was a bit unclear how big his cups were exactly, I just do a good handfull instead of a cup(also the plants I grow usually like it a bit lighter, so my handfulls are probably a bit smaller as the cup, but that's good in my case).
however I'm not sure chickenshit is as easily available everyewhere in the world as it is around here, so that's why I'd advocate to learn a bit about how nutrients work, and use that knowledge to make your own recipe from ingredients you can get locally and cheaply. so not just throwing in random stuff, first read a bit about how different nutrients work and interact. but in the end, I think nutrients and fertilizers don't need to be that exact. it's like cooking vs. baking, in hydro indoor I can imagine it might be more similar to baking, but outdoor using organic ammendments it's more like cooking, it won't instantly faill if you throw in a cup more of this or a cup less of that.
about cooking(resting the substrate), I think it's situational. it might depend on the specific ammendments that you use, but with chicken shit I don't 'cook', since chickenshit has quiet some quickly available N, and that flushes/leaches out pretty easily with some rain if there's no plant in it. so in case of chickenshit I think it'd be a waste of N to 'cook' the mix. but if you're using a lot of ingredients that need some composting/breaking down, I can imagine cooking might be usefull.
