You can use the fertilizer, but definitely, DEFINITELY dilute it, by half at least for the first dose, then personally I'd alternate that with clean water if going with soil amendments. One thing that's never mentioned here, but should be, is that nitrogen can be found just in water in the form of nitrate (that's essentially an end product of the oxidization of ammonia, which is often the means by which ferts get nitrogen).
As for the others, they usually tell you how much on the bag, and they're assuming the plants are being planted in ground. For instance, my blood meal says to use something like 1 Cup meal for every 20'sq. scratched or turned into the surface of the soil about 3" deep (this is from my faulty memory, but bear with me). I'm planted in pots, so I roughly calculated how many cubic feet are in a 2'x10'x3" plot and used the appropriate amount for how much soil I had (I had 4 cubic feet of soil). That adds up to 5 cubic feet (see this
volume calculator, and remember that 3"=0.25' when figuring).
All of these products, and more (you should check out Subcool's Organics, and I can't remember where the soil recipe is, but oh well, you work with what you've got, right?). Bat guano is another one that's good to just mix into the soil. Worm castings are also good to mix in, and for clay, these plants that I've grown seem to appreciate sand. Their roots seem to grow through the sand more easily than loamy soil mixed with perlite.
Crap, am I making sense?
AHA! Found it.
https://www.rollitup.org/subcools-old-school-organics/44686-subcools-super-soil.html#post478850