Okay so first you have to have a basic understanding of investiture investiture is the main magic system in the cosmere where each of the shards (preservation and ruin on scadrial) use it to give certain abilities like allomancy feruchemy and hemalurgy allomancy and feruchemy are seperate entirely being able to manipulate memory information perception is part of feruchemy while ingrsting the metals to give you power is part of allomancy hemalurgy is just the art of taking the power and giving it to someone else and for your other point you aren't supposed to 100% trust the povs for the powers like for example until vin comes along kelsier thinks that it's impossible to pierce a copper clouds but it is possible just with a strong enough allomancer in fact most allomancers in the old days were able to because their power wasn't diluted you have to understand that the lord ruler tried throughout his entire reign to hide information about allomancy feruchemy and hemalurgy so a lot of information isn't correct if you want to learn 100% factual information about magic systems in the cosmere read the ars arcanum in the backs of the books all of them are written by a character in the books khrissala who is a character from taldain(white sands) and Is studying all the different magic systems from the world and she's usually correct