Hey Con
Welcome to IIS. Well done on the 8" dob the ideal starter scope!
With filters try this link
http://www.lumicon.com/astronomy-acc...d=1&cn=Filters
It gives a rundown on the various filters and what they do. Straight coloured filters are used primarily for planets to improve contrast of certain features. I use an UHC neb filter to try and improve contrast in faint nebs and an OIII to help with planetary nebs. Find them useful.
Unfortunately with EPs you really get what you pay for. Having said that I observed for 2 years using just a 25mm plossl and was quite happy.
I am a big fan of the 24mm Televue Panoptic but that is still a $300+ ep. If you see one second hand - grab it.
Televue make plossls that would have a better build quality than the $30 jobs, but cannot comment on the views.
Malcolm