Yeah these guys are all right, the thermite is normally started with a strip of magnesium as the heat given off when it burns is nearly always hot enough to kick the reaction off. Thermite will melt metal, its used to weld together railways tracks that have broken as one of its applications. I wouldn't mess.
I intend to do it in sand... no need to worry about melting the container.
Magnesium strips are actually not that hard to get. Camping stores and such sell "emergency fire starting kits" that don't work - but the block that you're supposed to shave is made of magnesium. Sparklers also contain magnesium. Anyway, I'll be safe about it.
Thermites are rather harmless, just make sure you don't need whatever is beneath it :).
As for ignition, good luck. As mentioned a magnesium strip will work but it's hard to find. A few sparklers might do the trick though.
To make it easier for yourself with the aluminum powder you could put small pieces of tin-foil in a coffee grinder.