If you go with the Marlborough Sounds Adventure company (I think that's their name) you can go without a guide or experience we did a couple of years ago (see Heels 2005, whoops it hasn't been published yet...), and I'd recommend it.
In seriousness, you hire boat, paddle, life jacket, they tell you how to tip it up the right way if you capsize and off you go straight in to the ferry lane. After some fast paddling to cross the ferry lane you are in Queen Charlotte sound proper. It took us two easy days paddling to get up to Blumine Island and camp (we also camped in another bay whose name eludes me) . It must have been very easy days because on the last day we split up, some got the water taxi back but me, Hannah and Ben Clendon paddled back and it only took us 4hrs (admittedly via a much more direct route).
So I'd say experienced people might help but don't let it stop you, it didn't stop us and only one person fell out ... twice.
Richie