More like 3 or 4 inches, I believe. There are several kinds of "glass catfish" but the most common one is pretty small.
I doubt feeding would be a problem, assuming the glass cats are acclimated and eating well before introducing with other tankmates. I have a school of 9, and I had to feed live brine shrimp at first to get them eating well. Now they will take flake food right from my fingers, and will pick up (although fail to eat) shrimp pellets, which are intended for cories. They eat so well that they splash me and swarm to the surface if I even open their hood, certain they will be fed.
I see no trouble with angels, in general. My LFS has a display tank with angels, glass cats, tetras and cories.
Get as many as you think you can fit in there and maintain good water quality. I don't think a small shoal does these wonderful fish justice. The 9 I keep are in a lightly planted 20 gallon tank, with several other small fish, and no water quality issues at all.