If you do the tp-thing please let it drop a log when it happens xD also random tp could glitch you out or arenas or into a hill lol. I think two spells would be fine also AOE nullum incendium plez xD
First, why do you want it to drop a log? If I did make it drop something, I think it would be cool to be a Magma Cream or something that when stepped on sets you on fire or gives you slowness or something so the spell kinda melts you from one area to another.
Second, your concerns. Tping out of an arena I think I could deal with if I look at WorldGuard or something. Suffocation isn't an issue; Make a list of all blocks within x radius, for each block check if the two blocks above it are air, if so, add it to a list of possible locations. I will keep the radius I think a maximum of 5 radius to avoid too many issues as well. Also, two spells sounds like a good idea.