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Narrow bandpass nebula filters are the only ones that will do anything spectacular for astrophotography. Not much will help with galaxies AFAIK. A general purpose nebula filter like the DGM NPB (you can order from dgmoptics.com) is where I'd start. Baader/Lumicon UHCs will do a similar job (so I've read) and you can buy them locally. Then later on, if you want to get serious with nebula photography you might invest in filters aimed at emission lines of specific elements. This way in one shot you can image oxygen, in another hydrogen, for example. Theoretically you could even distinguish between different states of ionisation, but I'm not sure if that is something amateur equipment can do...
IR = infra-red. Whether you need it or not depends on camera + filter characteristics (the infra-red spectrum is very broad compared with visible). Try without and see what happens.
Grain of salt: the only bit of astrophotography I've ever done is stick a film SLR on a tripod and point it at the Moon.
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