congratulations for your decision to keep cichlids. In my opinion, no other fish family is more interesting than cichlids. Despite the fact, that cichlids (and most other fishes, too) do not need high aquariums, I want to say, the height of your tank is not optimal for mbunas like Labidochromis caeroleus “yellow” and Chindongo saulosi. Both species are not the kind being described as “peaceful”. 12 inches is little bit flat for them. If your heart belongs to east African cichlids, most of the smaller species of Lake Tanganjika are better suited for your tank. I mean fish like Neolamprologus leleupi, N. brichardi, N. buescheri and all species of the genus Julidochromis. Start with 3 or 4 different species and put 4 to 5 specimen of each species in juvenile sizes in your tank. They will spawn and within 1 year your tank will be fully loaded, probably crowded.
As I could read in the link, the sand from Canadian Tire is excellent for floor ground for aquariums, provided, the granulation is not too small. 0,4 to 0,6 mm is optimal.
Of course, you can use garden rocks. Important is, that there are many caves for the fish to hide and to breed. So don´t choose big rocks, with smaller ones it is easier to build hideouts. Place the rocks on the back wall ´til the surface of the water.
A canister filter is a good choice, but not the cheapest one. In most of my tanks below 100 gallons, I used to glue a pane 10cm from the backside and 20 cm in length. On the bottom, I glued a 8 cm high plane to avoid, that the gravel is falling into the filter chamber. Between the backside and the pane I put 5 cm thick aquarium foam, cut from a 50x50x5 cm mat. So, the first 10 cm of the filter chamber is occupied. Behind the foam, put a 1.000l submarine water pump (Resun or other), available by Ebay for under CAD 20$. If you want to have more filter substrate you can extend the glass pane and put more foam in the filter chamber. An advantage is, you can easily wash out and clean the first of the foam package and place it as last one after cleaning. So, all the good filter bacteria keep still alive during cleaning.
I hope, I could give you some advice for successfully keeping cichlids.
Please, forgive wrong grammar and spelling mistakes. English is not my native language and my schooldays, where I learned English, have been a long, long time ago. For the same reason, I used the scientific names for the fish to make clear, from which kind of fish I am talking about.