Your learning curve is only as shallow as ur questions. And u ask good ones. U cant really overfilter, bit u could cause too much current for certain fish.
Using a sump does not mean u have to drill your tank. U can,but not absolutle necessary. Im a new aqua head too, maybe 6 months or so. If i could offer some advice...its uber easy to take the advice of some one at a LFS and buy everything they say you "need".
Mr X and Rivercats are a wealth of knowledge. Soo many thing can be built or re-utilized. Do not fear DIY projects. As with anything research till ur bored, then re-research. It really helps me understand the theorys and operation of things. Think fish every free daydream moment u have. Ur on the right track.
But lets bring this back to original topic. Replacing filter media. When u go to pick up ur tank today, get a medium or coarse media bag, and about 300 grams of ceramic rings. I think rings have an amount to gallons of the tank. But with a HOB filter i think this should be ur best bet of esablishing a strong, transferable bacty colony.
Between your filter cartrage and its overflow, put a media bag with ur movable, permanent media. Im telling u...the larger the space for bacterial growth, the larger/stronger the colony, the less time spent testing/worrying/doing massive water changes daily/.
