There is already a Malawian 737-300 flying for Air Tanzania. As for where the 767's would come from, Gulf Air is due to replace their one's so I'm sure they would give ATC and the Tanzanian goverment a good deal on them. As for the ERJ's 190's, don't know much about the type but with the thin routes here it is actually the right size. Saw the demonstrator here not so long ago.
Money isn't a problem here, Tanzania is one of Africa's golden boys right now. Though a complete overhaul of the company is nescesary. Plus along with aircraft a large influx of cash is needed after the company was strip mined by certain people and companies.
The Domestic market is rather thin for ATC especially with the road improvement program going on. But the thing that ATC does have going is the fact that it still has a load of international routes which would be very profitable. Many consider these routes the only real reason SAA was intrested in ATC.