wow, thats a lot of fans, why not get just one 120mm fan? or yoru case doesn't fit one? Anyways, a filter is better than no filter at all but it will restrict air flow a little.
if your not afraid of modding you can fit 2x 120 mm fans in the front
also you can probably just barely squeeze 2x 92 mm exaust, im modding both real soon
2x 120 mm and 92 mm M1A panaflo's are gonna be sweet
on subject of filters, theres no real use to filtering imo.. i just clean out my case every 6 or so months or when temps are too high if you have your air flow balanced you should not have dust problems
www.svc.com has a decent selection of filters I believe. I am not famliar with that case but I doubt you actually have 5 intake fans so you probably don't need 5 filters. Filters are only needed on the intake fans, not exhaust. Unless you are really concerned about dust I would run without filters and just clean out the PC once in a while.