Good idea, but I think if you get only a 30 then the best you will be able to do is to make a good sized school out of your Black Skirts and Cories. There will not be room for that many more fish. Also, a 30 is really too small to have 2 schools that live in pretty much the same zone in the tank. However, here are some ideas.
Other fish that look a bit like Tiger Barbs, but are OK in community tanks:
Puntius pentazona Hey, they changed the name! Oh well, it is still a nice fish.
I would stick with Otos in a 30 gallon. Any of the small Plecos will still take up more bio-room.
Botia angelicus would do better in an even larger tank. They are social, and more fish this size means a larger tank.
Can you handle an even larger tank? Perhaps a 45 gallon, 4' long? If you can get one that is not so tall, but sticks out further from the wall then the bottom fish will be happier.
I could see stocking a larger tank like this:
8 Black Skirts
12 Pentazona Barbs
5 Botia angelicus
6 Brochis splendens
1 Bristlenose Pleco.
That is a pretty big bio load, but a healthy planted tank would be OK.