I agree you should stage the elements. I believe your filter should be pleated and be a basic type ($2-5). If you buy the really expensive filters (over $5) then they are quite restrictive and can cause all kinds of havoc on the system. Pleated 1" filters should be changed every 1-2 months. If the system duct work is not large enough to handle your system with a pleated filter then it should be changed or you can use a blue fiberglass filter as a cheap work around even though it is still not "right".