Question. Was it ever established how big a gun Sukuyo could make? I've gathered that it has to be man portable, but how big within those limits?
It was never established how big a gun Sukuyo could make. However, Kyouko and Mami have shown the abilty to make upscaled versions of their weapons in the anime and Sayaka's certainly showed that she can do the same in quest. It's logical to assume that the newbies all have that ability too.
By all accounts Sukuyo is Borderlands, the Magical Girl and there should be no upperlimit on how big a gun she can make, or how much gun she can cram into a gun. I would however, say that making anything that fires something other than bullets is probably doomed to failure. "Gun Creation" can only go so far after all, and even Sayaka's aiming hilts are just modified sword hilts rather than actual guns. However, she can more than make up for it with creative ammo creation for now.
Of course, the higher up you scale her guns and the more special ammo she fires, the more it'll cost her. Then again, her power is passive Damage Reduction so she's really only got her weapon skill to dump magic into.