They use them around here for ponds. No trick but alternate the seams on the rows when you stack them. Just get a truck load of bags of quikcrete and a truck load of bag handlers or your relatives to stack them. They bag quikcrete in 60 lb. bags which make them easier to stack.
I personally don't like the looks of bag walls, torn paper, faded paper, and think it is a waste of concrete but all you need is a good back. Reinforcing and anchoring is not typically used but I don't see where it can't hurt to add rebar like a normal job. I don't think water will get into and set up the concrete completely in bags that aren't under water.
If by sea wall, you mean the real ocean with wave actions, then you are looking at mulitple rows and anchoring and I couldn't tell you much about those.