Not sure about doing 2 pieces, they've only asked for one but it can't hurt to have another prepared in the bag
I've thought about doing a standard, Autumn Leaves maybe, melody, bassline, improv, melody type thing. Would definitely be over the 5 min mark too.
The school isn't open yet so I'm not too sure what type of music they do but I think they're trying to sell it as like a jam school so I think it might be quite rocky.
Dlloyd - lovin that vid, might try and do something like that. I've seen Marcus Miller do Come Together in a similar style, could be worth a go!