Are you going to do a freshwater tank? If so I think a sump is overkill especially if you have a good canister filter. Sumps are most commonly associated with salt water tanks and basically a sump is just a "build your own filter" in which case you don't need a canister filter or HOB filter - the sump is the filter. Usually it's a container connected to your tank on the back where you put all the filter media of your choice (I have biocube which has the sump built into the back of the tank so I don't need a separate container). Most aquariums with sumps have a bunch of slits drilled into the top of the tank (like the one you are thinking of buying) that makes the water overflow into the sump area connected to the back of the tank. The sump may contain a main filter like those sock things - which are just a very fine filter almost of polishing cloth consistency, water goes through the socks and into a different section of the sump which can contain the media of your choice - there is an exit to the sump with a pump and tubing (big tubing like in your canister filter) that pushes the filtered water up to the top of the aquarium and back into it. You can replace the media just like a HOB or Canister filter as needed and it's pretty accessible and easy to do.
BUT These days even many salt water tanks use a cannister filter because they don't have the cutouts in their aquarium for the water overflow - so they just send the water down through the tubing into the canister filter - which then pumps the water back into the main tank, hopefully all nice and clean. If you're doing a freshwater tank I'd silicone over any slits/opening in your tank (and hope it holds and doesn't leak water) and use a canister filter otherwise you'll have to keep the water level below the overflow section at the top of the tank or it will just spill on the floor. If the aquarium was used as a saltwater aquarium, especially for reefs it may be rather short and long to accommodate long reef shelves. Mine happens to be square which is really limiting when you try to build a reef without touching the walls of the aquarium (so you can clean all the walls) at 32 gallons it's just a little too big to be considered a nano saltwater/reef tank. Originally It's sump came with 3 chambers. Chamber 2 where all the media was supposed to go was really overkill in size and metal shelves prevented you from putting other equipment in the sump (like a protein skimmer, heater, UV sterilizer etc, so I spent a ridiculous sum of money ($70) to buy this cheap looking tall plastic piece with 3 or 4 shelves. This divided the second section of my sump into two section making 4 sections in the sump rather than three and supposedly doing a better job of forcing the water through the media instead of having it just bounce off of it (a problem many biocube owners were supposedly experiencing. So I will have a protein skimmer in chamber 1, chamber 2 will contain all my media, chamber 3 will contain a heater and eventually (once the tank is cycled and has been going a while) a UV sterilizer, the water will then flow to chamber 4 where the return pump will pump it back into the main aquarium. So again, it's like a really fancy filter all designed by you.
if I were you and had most of the parts for the sump and tank I'd give saltwater and reefing a try - knowing you'll probably have to come up with at least $500 or more to make it a functional salt tank, With live rock or "life rock", that's $100-$400 foe 20-40 lbs, then there is the cost and hassle of having to make and store some RO/DI water which will make the water completely without any solids ie., as pure as distilled water. To that water you add the special salt water salt in the correct quantity and use a device to measure the concentration of salt or density of your tank Then you cycle it and start adding a couple of fish (clown fish like Nemo being popular at between $15 and $50 each) and buy a couple of coral fragments "frags" at a cost of $15 to around $2,000 a frag (there are plenty of beautiful cheap frags - I guess the saltwater elite buy the expensive "rare" ones. Keep in mind the fish are a LOT more expensive and each coral has to have a specific amount of light and water flow so you have to research that all out so you know where to place it on your reef. Or get an Anemone (which can and will sting you) and also likes to move on the reef on it's own - at least they'll find their perfect spot on the reef. The clown fish is the only fish allowed into the anemone's tendrils without getting stung. This is because they allow the clown fish ONLY to clean them. So LOTs more cool things happening in a salt tank than a freshwater tank. The fish are more vibrantly colored and way more expensive than just about any freshwater fish out there) the corals are amazing and as the earth's corals are being destroyed you can think of yourself and other reefers as helping to keep them from ever going extinct. (of course some of the frags are stolen directly from the ocean reefs rather than being cultivated).
You can also get really fancy and purchase a small 10-20 gallon aquarium and make it a Refugium - which grows very specific bacteria - since I've never actually seen one I don't know much about the function of a Refugium but I bet every "real" salt tank owner has one. I bought some of the stuff for one but now that I have a Biocube I'm not sure how to attach it to it, so I'll probably skip it.
So why not give saltwater/reefing a go since your getting an aquarium and sump already plumbed for it? (it will also take every bit of income you have once you become addicted to the corals and the beautiful fish)
you said yourself its a bargin
