I have been asked to organise a school visit to Joburg with some trips into Soweto to visit sister schools thrown in!

What I need advice on is:

Suitable inexpensive hotels in the city that will sleep 3 or 4 to a room (for the kids).
Advice on traveling round. Can you hire minibus type taxis as I don't want to split the group up if I can help it.
Places to visit in Joburg suitable for teenagers.

I shall be contacting some specialist school travel firms for prices but I would like to see if I can do it myself as well to give me some comparisons.

Thanks.