The optimum temperature range for axolotls is 14-18 degrees celcius. Axolotls will 'tolerate' temperatures up to 22C as long as the water quality is excellent (warmer water increases the toxidity of Ammonia). If the temperature hits 23C, it's time to start putting
tank cooling tactics into effect. Temperatures 24C and above will cause stress to the axolotls, leading quickly to illness, and likely death.
Bare bottom tanks are by far the easiest to keep clean. Quite a few members of this site use bare bottom tanks and have no problems. Some axolotls may experience difficulties with traction on the slippery base of a bare bottom tank, and they can find this stressful. If this is the case (or you prefer the natural look) however, sand is also an excellent substrate, and makes for easy spot and removal of grot.
Axolotls do not care for light or water movement. If you have a lot of light in the tank, you need a lot of hides, so the axolotl can get away from the light, if the light is bothering him.
The many benefits of filtration can be found
here.
If the filter has a strong flow rate (water movement is stressful to axolotls) you have a few options at your disposal. You can diffuse the flow by use of a spray bar, or place an obstruction (plant/rock/etc) in front of the flow to break the current, or if the filter has an adjustable outtake you can direct the stream to the tank wall.
The Axolotl Site has a wealth of information on the care requirements of axolotls. In my signature bar, there are many other useful links as well - all well worth a read through.
Welcome back to the hobby!