Sumps can be dirt simple or incredibly complex. Essentially you need some way to get the water to the sump ( overflow ) and one or more pumps to put the water back in the tank.
You'll need:
A) Hang on back overflow, or have the tank drilled for an overflow or standpipe
B) sump - another tank or even a 5 gallon bucket
C) pump, or pumps, to put the water back into the tank
You can run everything to and from the sump if you want including the filters. You would then pull the water from the sump to the filter and then run the filtered water back to the sump, or up to the tank. You MUST include a siphon break or check valve in EACH path you have up to the tank or you will have a flood when the power dies. If you run all the pipes up to the tank from below you pretty much have no choice but to use check valves. This can be somewhat complicated but it allows for a completely clean display with no visible pipes or anything going over the sides of the tank.
IMPORTANT: Make sure the sump will hold ALL of the water that will drain out of the tank during a power failure. i.e. the level at which it stops either from check valves, overflow, and/or siphon breaks. This is usually an inch or two. If you forget this you'll have a mess to clean up later.
If you want to get fancy, you can do a "hybrid" kind of system. The sump would handle some things like the CO2 and heater and circulation. The canister filter could then have its own intake and return lines and the other pump can do the same for additional filtration.
Note on efficiency - Every time you have an air gap of some sort in the system you are using additional power. For example, if you run the cannister intake and exhaust into the tank directly it will be far more efficient and get you more flow than if you run the intake of the cannister from the sump and the exhaust into the tank. Why? You're going to be pumping "up" to the level of the tank and that takes power. An easier way to visualize this is to hold up your intake and exhausts and see where the water lines in the tubes are. If they're pretty close to the same height that's going to be more efficient than if you have a difference of a few feet that the pump has to make up.
For some this is more of an issue due to filters not always having the best flow to start with. For others it's a financial one when they start to deal with the power required for marine tanks to get flow. This is one of the major reasons you see prop pumps like Koralia for flow.
Based on what you've described I'd probably do something like this.
CO2 and heater in sump. You'll need to test your cannisters and see what you can get out of them. Get them running and run the intake in a bucket on the floor with the water level about where you think it will be. Raise the output up to the level of the tank top and see what kind of flow you get. If it's miserable, I'd suggest either another filter, or run the output back to the sump instead and get a better pump for the tank return. For better flow in the tank, you'll probably want to run a couple of returns to the tank. You can run these off one pump, or multiple pumps/filters. Experiment. If you're going to buy a tank for the sump, you may want to consider a wet/dry filter instead. There are threads here on their use with overflows and CO2.
If you do use the overflow/sump these may be sanity saving...
Hofer Gurgle Buster
Everything You Always Wanted to Know About Sumps, Part I by Greg Taylor - Reefkeeping.com
