I've never needed co2 on any of my tanks that had low-moderate light plants.
Didn't use liquid carbon, glut, not even ferts. -- All of those tanks have done perfectly fine, even without any surface aggitation, lighting is enough for most plants in the low/moderate light category.
I did just start co2 on one tank, and liquid carbon on 2 others, there has been a decent amount of growth rate change, but they all did well before.
--Sorry, I just really hate seeing the wrong info being put out there..
As for the SW/FW debate... Personally, I like the idea of doing fresh first. Learn all the basics, that way and if you mess up you're not going to lose a ton of money on the set-up and fish. SW is a lot more time consuming and expensive in the long run, actually even after start-up costs if you go the live-rock route.
But, I'm a bit biased, I love my FW planteds. I have only tried SW once and it was just too much work for me at the time, and that was after having extensive knowledge of fresh, I can only imagine what it'll be like for a beginner, even with all the help of AA and other forums