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It's worth noting that the slower the f-ratio of the unit (i.e. higher f number), the easier it will be to collimate and keep collimated. Granted, this is less important if the scope stays in one place most of the time.
Also, a slower f ratio will allow cheaper eyepieces to be used (within reason), and without extra gear such as coma correctors, for quite good results. The faster the scope, the more coma it introduces.
Filters: again, it's the exit pupil that matters. I use an OIII on a 60mm refractor regularly for extended low-power targets such as the Carina Nebula, viewed from the city. The tradeoff with small scopes is not whether an OIII or other filter will work or not, but the power limitations of the small aperture.
Form what I've read here so far, 8" does not seem a bad choice.
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