Need Skill leveling Help

I am thinking if leveling my formation's skill level of 4 with skill stack(4) is a good idea.
If not, should I try to go with (2)?

I usually level my formations skills without stacks until they hit 5-6 (in some cases even 7-8 )... and at this point I start using (4) stacks.
I leveled some skills to 10 without using any stack at all aswell already.

But that's just me... if you really want to go the "safe way" you should start early, maybe at a skill level of 5?

1 until lvl 4 its easy, just use one monster with skill lvl 1.

I usually get to 4 np. Secret i found is to use a sac with higher bp than your base monster. if not it might take a couple.
4-5 sometimes takes a couple of tries.
from 5+ i only ever use 5 stacks. Never seen those fail.
I have had 4 stacks fail.
A little more expensive to get to the 5 stack but cheaper than losing a 4 stack and having to make a new one.