Oh, salt. It is wonderful stuff. And yes, if you put too much salt in, it will mess with thier osmoregulation. Basically thats just a fancy way of saying that, due to osmosis, if you put a fresh water fish in salt water, it will "shrivel up and die" because all the water in the fish is diffusing to the solvent (salt) rich water out side thier bodies, and if you put a salt water fish in fresh water, it will "blow up and die" because the fresh water will flood thier solvent rich cells.
In short, laymens terms: don't use too much salt! Its bad.
Personally, I like salt. It helped my male betta after he ripped his fins (he though it would be fun to slip past the tank divider and beat on the female. He lost the fight...) and its also helped him in stressful situations.
I also have plants, and they don't seem to suffer any ill effects from the salt. I'm careful not to add too much, because I want to be able to add a little extra just incase my betta gets parasites or bacteria. But all in all aquarium salt is pretty awesome
As for the plants...I strongly agree with the java fern. Those things are wickedly hardy. I've been pulling it out of the gravel, taking it long train rides (I'm a college student, with no car), and generally neglecting it, and it still thrives. Its even decided that it wants to have babies (I know have lots of little java ferns in my tank).
Another good plant is bamboo. These plants are also hardy. Like the java fern, they don't need direct light, and so are perfect for a bowl or tank. With my bamboo, I just stuck them in the gravel and they took up residence. They're still bright and green and making my tank look good.
I've also tried a couple other plants. Back when I lived at home, I had a nice ten gallon. I tried to plant anacharis, money wart, some plant that had the name scarlet in it, and some plant that had the word wisteria in it. These plants didn't work out as well. I think it may have been the metal band that weights down the plants. There's a very fine area of how tight the band can be. Too loose and the plants float away. Too tight and the plants rot. I couldn't find that happy medium, so I always had either entire stalkes of plants floating all over the place or mushy bits of rotted stems clouding my tank. I finally gave up on everything except my java fern.