Don't worry about RGB color filters. I bought that really cool Celestron kit with the various lenses and color filters and never use them. The case looks cool though.

You could pick up a moon filter, because as it gets fuller, it gets way brighter. Celestron has a moon filter on Amazon for $17. http://www.amazon.com/Celestron-Filter-Moon-94119A/dp/B00006LSVL?ie=UTF8&psc=1&redirect=true&ref_=oh_aui_search_detailpage

Don't expect million dollar views with your telescope however. Even under the best conditions most deep sky objects will look like green or smokey gray blobs.

You should have problem exploring the moon and the planets. Jupiter is well positioned now in the early evenings. Saturn and Mars come up later.

As for other sites, I've bought a bunch of stuff from CloudyNights.com's classifieds and my local CraigsList.

Have fun.