Sock yarn substitutions

#1

I was supposed to use brown sheep nature spun sport for these socks for my father, but the yarn lady sold me cherry tree hill & koigu instead.
it says in the pattern to use size 1 or size to obtain gauge, but the website that sells bsns says size 5? and my koigu label says size 3 (the other says nothing!)? so I can use a size 0 and that’s fine?
can I completely disregard labels in general when I’m knitting socks & do you think it’s more important to get gauge or how tight the stitches feel when they’re knit? can they be too tight? and how do I know whether it’s too tight? is tighter better for socks?

thanks!

#2

for KPPPM or the Cherry Tree Hill that looks like KPPPM (single strand), I’d use a 2, 3, or 4.

#3

both my yarns are fingering, but the pattern is sport?
is this bad?
why is the pattern yarn thicker but the stitches (according to the gauge anyway) smaller???
I am so confused - how can anyone knit smaller when I am pulling the yarn so tight?

but - aside from that - so you think I should just recalculate all the inc and decr and all that? is it hard for a sock?

thank you!