http://m.liveaquaria.com
That is a great website to search for future inhabitants. They have a lot of info on individual fish from diet to tank requirements. They list compatibility as well.
I don't believe there are any dwarf angels suited for a 30g. As for chromis you will be hard pressed to find anyone on here that will say it's ok to keep 4 in a 30g, personally wouldn't try even one in a 30g. Not all but a lot of sand sifters tend to eat all the beneficial living critters out of the sand bed then slowly starve to death. That website I linked will have all that as well.