I'm not the best with plant names...I tend to purchase them locally and they're not labeled....if they live, I get more, if they die, I purchase something else, lol! Peachii is the plant guru and she knows *all* the names, you might want to send her a PM and ask this question. :)
But, in the meantime, this what I've found about plants...
You always end up needing more than you think you will, lol! It also depends on how "full" you want the tank to look and how fast. I'd definitely recommend *big* stem/bunch plants for back ground stuff, with a few shorter/smaller things in the front. You can have a fairly full looking tank pretty quickly this way and not spend an arm and a leg on the "short" stuff.
Stem plants I like:
rotala (comes in lots of types, all are pretty easy to grow)
water sprite (I've only had Pond though, so I don't know anything about the smaller aquarium version, I've heard it can be hard to grow. The pond stuff grows like mad though!)
moneywort is usually pretty easy, though sometimes I've had it melt on me...no idea why.
water wisteria is always great because it can be planted or float, which I love
I recently got some cardamine, and I really love the look and delicacy of it. :)
Vallisneria grows quickly and sends out shooters like ever two days... lol!
narrow leaf anachris is also nice, grows like crazy, and is a finer/prettier version of regular anachris. Can also float.
As for small stuff, I usually stick with java ferns and tie them to rocks and display them in groups of three or so in the front of the tank.
Oh, and I have decided that I don't like frogbit and duckweed. :P It gets everywhere, tends to make it hard for me to feed my guys (food gets stuck in it), and it's just a pain to deal with when you're moving stuff around or putting in new plants. :P What I DO like is salvinia, red root (these may be the same things?), and floating leaf flower. These are great for providing betta cover (because they love having surface level places to hide under), suck up lots of ammonia, and they are easily taken out and put back in when moving stuff around or cleaning. :) They grow in little bunches about two or three inches long, so they're easy to get in and out. :) And they're easy to keep in one spot so you can have an open area for betta feeding. :)
In terms of how many you'll need for the tank to silent cycle...that's up to you, your fish, and your plants. If it was me I'd purchase however many you need to make the tank look like you want, or however many you can afford, and then do water tests. If things are at 0 across the board, then you know you're good to go. If not, then stick in a sponge filter and use it as backup for your cycle until you can get to that point. A lot of it depends on what plants you get, how big they are, what your fish are putting off, how much uneaten food stays in the tank, light...the list goes on and on. Safest option is to cycle the tank with a sponge, then start sticking in plants and go from there. :)
As for snails, I tried no snails because I had a pond snail problem...which I then purchased assassins to kill off...and then I had no snails, and I ended up with a nasty algae filled tank and some dead plants. :P I'd definitely say you need snails. :)
The way snails (and shrimp for that matter) work is that they're cleaning up your tank. It's much harder to siphon and gravel clean a planted tank, so you're going to want some cleaners in there to take care of it for you. :) Snails are great in terms of cleaning up excess food, eating any dead material off your plants, and taking care of algae. Snails, again, depend on size. In my 20g's, I've got two bettas, two mystery snails, and an unknown number of ramshorns. The ramshorns were unintentional, they came in on plants. There are a good number in there though...I'd say at least fifteen. :) But, again, you don't want to have too much in there until you get cycled and steady. I'd put in a single mystery snail, and probably three of four ramshorns to take care of any cleanup you need done. :) Some shrimp types also work...but I don't know almost anything about shrimp, that's a question for someone with far more knowledge...or you can google it. :)
I hope that helps! :)
Oh, one more, I order my plants from Tricker, and I've always been *really* pleased with the *enormous* size, quality, and price of what I've received. :) We're talking wisteria that's a foot long...and I ordered babytears once (not the potted ones, the ones from the actual ponds on site, and I swear those swatches were eight inches long and four inches wide...I was astounded at what I received. :)
Also, look around the site, they've got some really neat stuff. :)
I hope that helps! :D