[drache]

a 20G long should be fine for a garter
I have three in a 29G and that's got the same footprint.
mine are not fully grown and they will get to move pretty soon, but you're talking one snake, right?
of course more is better
my garters love to hang out on branches
although I keep my cages pretty minimal in other ways, I always give them branches to hang out on
it has the added advantage that I don't have to be so exact with the temps because they can pick how close they get to the heat
with the thermometers, I don't know either
people have their favourites
I haven't found a thermometer that I absolutely trust to be accurate within my price range
when you buy, look at all the ones they have in the store and pick the one which has the average temp of all of them (does that make sense?)