Hi Simon. I work with small aperture too (smaller than yours!), and find that a variable polarising filter is very useful for the moon, especially when showing other people. Brings up the darker maria etc, and easier to look at & appreciate detail. I have an OIII filter, but it's not really that useful. However, it does isolate the brighter nebulae at our aperture, but light loss works against it. Forget it for dimmer stuff. I own & have tried various coloured filters. Using them on planets as recommended, I have noted some slight benefits (or did I imagine it?
), but can't say I've been overly impressed. Hope this helps!
Cheers -