Sorry for answering so late ...
I have knitted only twice a bottom up cardigan. It was a Japanese pattern which consist mostly of schematics which I find much more helpful than written instructions.
And you are right youtube is such a good help :-D
And to the tension/gauge (I hope it's the same): For a long time, I also thought it is not helpful, but as I knit and crochet super loose, I learned to do a tension square. If I want to make a bought pattern, I always must change the needle/hook sizes.