Hello and welcome

1. Zilla critter keepers are great! I own 1 myself, a 20 gallon long.

2. Both would be great, but if that's not feasible then I would recommend getting the basking light. In the wild garters love to bask on rocks and branches soaking up the sun's rays for warmth and to aid in digestion. If you were getting an albino garter snake then I would say you should get the heating pad because most albinos are sensitive to bright lights.

3. I would recommend in investing in a temp gun with a probe, something like or similar to what ProXimuS has. In my opinion these are more accurate than other thermometers, analog or digital.

4. Humidity should be anywhere around 50-80%, is good in my opinion. The humidity should be above 70% when your snake is entering opaque phase in order to aid in the shedding.

I use filtered water from the kitchen sink and add a couple of drops of ReptiSafe in my snakes water bowls.

P.S. If your friends flake out on the snake you can always check the forums classified section for garters up for sale.