Welcome to Tropical Fish Keeping forum.
Now, first off, a 10g tank is not very large, so don't let its appearance fool you. I know that all tanks looked "big" to me when I was getting started, but I quickly found out how small most of them actually are.
This leads into the next issue, which is what you need, because some of this depends upon the fish. For a 10g, my choice of filter is a simple sponge and air pump. But if the tank is in a room where noise is an issue, like a bedroom, air pumps can be noisy. A small internal filter would be better in that case.
Heater is needed, buy a good one; the most important piece of equipment is the heater, because if it fails it could mean the loss of all the fish overnight.
The sort of fish that will work in a 10g are going to be small fish that do best in a planted tank, so this brings us to the light. Least expensive is incandescent (screw-in bulbs) and with two Daylight CFL bulbs you can grow lovely plants. I use this on my 10g and 20g. Fluorescent tube light is more expensive, but works fine. Then we come to the LED lights which will be much more expensive but long-term they can save you. Finding good planted tank lights is a bit more difficult with LED.
Substrate. Fine gravel or sand works best, for fish and plants. I would suggest sand in a 10g, as your substrate fish (catfish) will be better with sand. A bag of play sand from Home Depot or Lowe's works fine, for a few dollars, with sand left over for the next tank. And there likely will be another tank, what we term "multiple tank syndrome."