does it make a difference to use pots at lvl 1 than 20??

Yes because lets say at level 20 you would need 20 life pots, if you use it at level 1 you would need something like 120 life pots to max

But other than that.. not really... Just really risking to waste some pots

The only one that doesn't change is def. I mean there are classes that max out at 25 def (robe/leather) to a knight which maxes at 40. But def is fixed for every class. No such thing as a variable def roll. Every other stat varies.

dont pot lvl 1 chars..
lvl 20 stats are random, so get a good hp roll

As example on knight you can get even 49 or max (50) atk roll on lvl20! There's no point to max at level 1. If you don't really care about hp/other stat rolls.. You can pot defense at level 1. Not suggested to pot others