For an easy, fast grower try watercress. Just pick up a bunch from your local grocery (doesn't matter if it even has any roots) and tuck the sprigs in between the rocks. You'll be amazed how fast it takes off. It does like moving water though so pick spots where the water is flowing, even slowly.For a first year pond and bog what would be a good choice for a fast growing easy to grow plant I don't imagine there will be a whole lot of nutrients
We did find that we had to feed our marginals for the first year or so - as you said, there just aren't a lot of nutrients in new pond water. They were growing, but they just weren't green. They looked a bit anemic. So I added some iron around the base of the plants that looked like they needed it and I even stuck some aquatic plant fertilizer tabs into some of the roots to give them a boost. By the end of our second season, everything was completely on it's own and growing like crazy.