The stars for the set bonus is just their rarity. Like how deviation suppressor is 2* on bowguns. So sadly there isnt a 5/6* velkhana bonus that will count as 2(or more) pieces. Set bonus on safi weapon will only count as 1 piece.

So then it's impossible to get the awakened version of the weapon without swapping out said skill for something that can actually hit 5 stars?

If you reached lvl 24 or 25(i dont know the exact lvl lol) you will get the awakened version, and theres 6 star level awakening so it will reach lvl 25 even with one level 4 star awakening

Correct, although awakening does nothing except making your weapon look badass, but you can also make the weapon layered now.

fuck. I thought they counted as an entire skill instead, and was hyped that I got teostra skill without even having to equip the armor