What size UltraTherm would you recommend for a ten gallon starter tank?
The UTH needs to be 1/3 the size of your tank and goes underneath the glass at one end. It should be regulated with a thermostat at 85°. The cool side will be about 75°. You will need a probe thermometer also (some thermostats have attached thermometers, most of us I think use the yellow ones that are cheap on eBay) and have the probe stuck down INSIDE the tank directly over the middle of the UTH. Cover this with substrate and put a hide over it. Some people use hot glue to stick them down, I use the suction cup that comes with it and put a heavy rock in the corner over where the wire starts to come up and out of the tank. Just check it if the temps seem off, I have had the probe pulled off the glass a couple of times.
Make sure you have a hide on each end at least, and a few in the middle or some leafy groundcover (plastic or silk plants work well) especially if they are little. The more comfort the better, and you can use toilet paper tubes flattened at one end and dug a bit into the substrate or toothpaste boxes or anything disposable or cleanable. It doesn't have to be expensive or pretty, just functional!
As for the aluminum foil, it doesn't matter which side is out. It is only there to prevent the very sticky side from touching anything and rendering it impossible to move, and it isn't flammable like paper. I just pull a sheet of foil twice as big as the UTH, lay the UTH sticky side down in the middle of he foil and fold all sides around it. Then you can use tape to stick it to the bottom of the tank. If the foil rips when you remove it you can always just stick a patch on! It definitely isn't about aesthetics.
Here is a pic of the Reptitherm, it is a thicker pad than the Ultratherm, and I don't have experience with the "stickiness" of Ultratherms. This is good for a 10-20 gallon tank, so when you have to upgrade you can just peel the tape off and put it on the bigger tank.
http://www.tarheelants.com/wp-content/uploads/2012/11/6x8-heat-mat.jpg
Would anyone who uses Ultras over Reptis do anything differently as far as wrapping it with foil? Does the Ultra come off easier without damage?