I've only dived Tofo, so I can only give the heads up for that area.
We flew into Jo'burg then travelled by bus through to Maputo. We stayed in a backpackers in maputo, Fatima's, who get a local shuttle to pick you up and take you to Tofo. It was an epic trip and as soon as you leave the backpackers, the bus is taken round the corner and crammed to capacity. Live and learn, I think we got the greyhound or similar on the way back, which was much more civilised and you didn't have to worry about your dive kit getting nicked out the trailer.
Waters temps were icy. I think 17-20 degrees. Not mega cold but we had flown in from Thailand and were shivering in 5mm wetsuits. It does warm up towards monsoon season (Feb?) but expect the water to be bracing.
Due to the currents, most dive sites will be negative entries, if you ears aren't up for that, then tell the guide. They normally run a leader/sweeper system. Where one DM rockets to the bottom and the sweeper deals with all the people who descend slowly. There is a towed buoy line to follow as most dives are drifts.
Beach exits on the RIB are s**t scary. Be prepared. Launches are equally hair-raising. 9/10 nothing goes wrong, but the odd flip isn't uncommon.
It is a Malaria region, so prepare for that.
I'm not selling it am I
Fortunately the diving is stunning. A good selection of pelagic life, Mantas, Guitar Sharks, Leopard Eels (?); impressive amounts of shoaling fish, stunning topography. And if you're lucky a whaleshark on the SI (take your snorkel)
Food is excellent, I think I became addicted to mataba curry. Beer is plentiful. Avoid the Tipo unless you like drinking petrol and coke (and enjoy blistering hangovers - it is cheap though)
There's a few dive shops on the strip. I'd recommend nitrox where possible, a lot of the stuff is in the 25m range.
Surfing is possible too.
