the blenny will be fine. Your tank is big enough. He's a jumper though.
They should be fine in QT as long as the angel is small (more for her sake then to worry about the blenny). I'd use black pvc
, it might make the blenny more comfortable - color wise.. get some height too and the angel will prob hang mid-tank.
I've used a 10g for qt forever. Gets crowded sometimes but then I think back to what they were in in the lfs