When I put my sand in I put the filter on and all the media including carbon, sponges, and so on where in the filter as it came. It's still running exactly the same now, some people will say not to bother using the the carbon on a daily basis but I don't see any harm either way. My tank has been set up for a few months now and is cycled and doing fine.
As for the temp when I had my tank I too had 2 300 watt heaters both set to 26 degrees c. I was fillings the tank with a hose through the window whilst filling with buckets of warm water at the same time so it only took around 4 hours for the thermometer to read 26.
Set both of the heaters to 26 and put a heater on either side of the tank (alone the back). That way you get no cold spots in the tank and heat is spread evenly. Also that way if one day one of your heaters failed you've still got a 2nd heater in there set to 26 as a back up.
I don't use the internal heaters anymore as I didn't really trust them. Iv known them to fail so you either end up with dead fish because of the water going cold (if you only have one heater in the tank) or the heater can actually go higher leading to boiled fish... Not good either way. Not saying this will happen but I wanted to put my mind at rest. Plus I keep big cichlids which were always bumping into them lol
So instead of running 2 300 watt heaters I now use a single 300 watt external hydor heater which fits on to your external filter inlet pipe, the water then comes through your spray bar or what ever you have and is pumped around the tank. Iv set it to 26 and it's always a perfect reading on the thermometer

iv put the thermometer on the opposite side of the tank to the elbow of my inlet pipe (iv taken the spray bars off for increased flow) just so i know the heat is getting all around my tank. I'd advise one to anyone that has an external filter. more efficient and less clutter in the tank
