Some Questions.

[MKLKT]

If you're talking about the white colonizing feather dusters then no they don't get to be very big, they just multiply like crazy. The coloured ones can get bigger but the sizes aren't going to be dramatic. Coco worms are about the fanciest ones and can sport pretty massive plumes.

Kelvin rating on refuge macro is fine whether 6500 or 10k, the amount of flow/placement and nutrients has just as much of an effect.

I have a small baggie of random shells from past snails/hermits in my tank; when I frag some of my stuff I'll let you know and you can have the shells, too.