Hi Ken
You certainly have to get your timings right to navigate into, out of and within the Morbihan, as there are very strong currents, particularly in the entrance. However, with careful planning it is all pretty straightforward. Depths in the main channel, all the way to Vannes, are not a problem; you go in with the rising tide and time your arrival at the lifting bridge for opening time (although they always seem to be 5 or 10 minutes later than advertised). There is a waiting pontoon and the Capitainerie sometimes come down in a dory and allocate berths before you pass the lifting bridge. If you like old cities, Vannes (old town) is well worth a visit.
There are lots of places to moor on a buoy or anchor, plus the pontoon at Iles aux Moines I mentioned above. Again, depths are not a problem if you are careful. We draw 1.95.
For swell, Magicseaweed is one useful site (http://magicseaweed.com/France-MSW-Surf-Charts/2/). Another is http://www.surf-forecast.com/weather_maps/France. We have found at 2m it starts to get uncomfortable. Below 1m is good!
One tip for the Raz – try to avoid wind over tide and particularly wind plus swell against tide. In 2008 we were half an hour past slack water with a NW wind( 3-4 only) and a 2m NW swell against as we were heading north and the there were 15 foot waves in the Raz. Last year, though, we arrived early, more or less at peak flow but with wind, tide and swell all going our way and the ride was fine.
Do your planning carefully and you should have no problems.
Best wishes
Roger