The heat mat totally depends on the species of snail and the temperature in your house. The "normal" giant african land snail,
Achatina fulica, is fine at room temperature (21-23 C), although you might need something to keep them warm at night, but
Achatina achatina like it at 25-30 C, and I've heard
Achatina reticulata,
Achatina immaculata and
Arachatina marginata like it warmer as well. Food wise, sweet potato is apparently very good for them, although it makes their poo orange! There's a list over
here of foods they can have. Coir seems to be the best from what I have heard, but whatever substrate you use, it needs to be kept damp, as snails thrive in humidity. Spraying once or twice a day is usually enough.
... Most of my knowledge about snails I picked up by reading this
monster of a thread over on a reptile forum (I end up reading some weird things
), but there are slightly smaller places to start, like
petsnails.co.uk. There's also a
snail forum 
There is someone on this forum who owns some
Achachatina marginata, who has posted a couple of threads about them too:
Introducing the giant african land snails - Margie suts (pic heavy)
Giant African land snail setup
Oh, and by the way, you think you are strange, well I don't even own snails (or reptiles, for that matter!)