Hmm if you want colour, its probably best to stick to the livebearers like platys, guppys, swordtails etc- as far as i am aware most killifish are semi-agressive or agressive fish and i don't really know enough on gudgeons to really say.
The ghost catfish would be better once you have a cooler tank for your dojo loaches, as these catfish do very well at the cooler tropical temps also etc
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The tiger barbs will limit your stocking options to a certain extent- there are a lot of colourful types of gourami's for example that could go in your tank if you got some tall dense planting in it, however tiger barbs have such a reputation for nipping the "feelers" on gourami's i wouldn't feel comfortable advising any gourami's for your tank with the tiger barbs in it.
Actually! I've just remembered Rams, they are an unusually peaceful type of small cichlid, they are rather peaceful fish and should be good for your tank if you add some dense planting to it;
http://www.thetropicaltank.co.uk/Fishindx/ramcich.htm
Rummynose tetras would be fine, just get at least 8 of them if you do get any so they can shoal properly, although i definately wouldn't advise discus (too specialised and needy fish, you really need to devote a large established planted tank to them to have any real success, most community fish aren't suitable as tankmates for them).