I'm thinking about doing a trip next year, in august/september which will combine safari and beach. I've got the safari-bit down, and it will be a five-six day trip in the Kruger area. But the beach part I can't seem to wrap my head around what will be the easiest good place to go. I've been thinking about Mozambique, around Maputo, but there's so many places. What is the easiest way to get from the Kruger area to Mozambique? And where should we go in Mozambique? We have a week +/- there.

Easiest way to get to Mozambique from Kruger area? Drive - you can get to Maputo easily in one day and it's good tar all the way.
Where to go in Moz if you have a week available? I would guess Tofo. If you go to Maputo you'll probably want to spend a day or so there and Tofo's a day's drive each way so that would leave you a few days to hang at the beach.
If you want more peace and quiet than Tofo offers then any one of the lodges around Inhambane/Tofo would fit the bill. Not all are accessible by 2wd so your choice may depend on your wheels. Otherwise, there are plenty of lodges on the coast between Maputo and Tofo so you should be able to find something to suit your taste/budget. Same questions of accessibility apply though.
One possibility a bit closer to Maputo might be to consider Inhaca. Never been there myself but I'm told it's nice and it saves you the drive to/from Tofo if you want to maximise your down time.

We stayed in Chidenguele, just few hrs north of Maputo, it has got a beautiful beach that goes forever in both directions. The owner of Paraiso Chidenguele (well run resort/hotel right on top of the dunny beach) where we stayed gave us an upgrade to a fully equipped chalet for the price of a double room. There is a bit of a sandy drive since you have to go off the main road to get to the beach, but all doable with a 2 WD vehicle. There are of course other accomodation options in the area and close to the beach as well. Don't underestimate the road distances in Mozambique, also factor the speed limits at every village and settlement, it will slow you down considerably. Reconsider driving all the way to Tofo, its a long way if you have a week, as Boomslang said: day to pass Maputo, day or more according to our recent trip to Tofo, times two and you have four days consumed by commuting.
Enjoy Moz, it is an amazing country and it only gets more beautiful the further north you drive, but you need more than a week to do this.
From what you wrote you do not seem to necessarily want to go to Mozambique, but you do want to have a beach holiday. I would suggest that you go south to Umhlanga, just north of Durban.

I realise that a week is only a skall taste of Mozambique, but it's a start. Thanks for good advice.
Rudi K; Durban area is ond of the few areas I haven't been to in SA. . How's the water temperature there in september?
Having spent my youth swimming in the sea around Cape Town, I would say that at any time of the year swimming in the sea in the Durban area is like having a luke-warm bath.

I forgot to mention that almost all the beaches along the Moz coast had tons of jellyfish, except for couple of places north of Mozambique Island and the beach inChidenguele (but this one has a very strong surf). Tofo was full of them both the beach and the water and some people were getting stung by them/ We were just there in Oct, not sure if they appear earlier in the season aug/sep when you are planning to go