: Water Wisteria, Water Sprite, Anacharis, Cabomda, Valisneria, Crypt's, most Swords, floaters (duckweed, salvinia, red root floaters, etc.), Sagittaria, Rotala, Ludwigia, Bacopa, Dwarf Lilies and some more that I know I'm probably forgetting.
Depends on what you want to do, if you want to go NPT then I know Miracle Gro Organic Choice Potting Mix is a great way to go and then you'd just have a sand or fine gravel cap. Or you can use Eco-Complete or some other enhanced substrate for plants. With Eco-Complete you don't need a sand cap or anything, although many mix it in with gravel or sand to cover more ground and you don't have to buy lots of expensive stuff.
that's more a personal choice really. You definitely want something adjustable though, never do non-adjustable, it's just not worth it. I like Hydor heater's quite a bit, Eheim is another great brand, even Aqueon adjustable ones are fine, Marineland and more. I know Hydor is most cheap out of most of those options and can be found cheap at drsfosterandsmith.com or maybe ebay as well.
Also depends. For NPT's you don't need a filter technically but doesn't mean you can't have one. Sponge filters are wonderful if you don't want something with a lot of current but AquaClears have been voted one of the better ones since they are so highly customizable. I can't say about Canister type filters though, I know some use them as well.
Best Tank Mates
If you're looking to move your sorority to the 55, I suggest highly to get more females than just six. Other's have had issues where it's just too much space for the girls and whenever they meet up, it's like they're meeting for the first time all over again and aggression becomes very bad. So bumping numbers up to 15-20 would be optimal. Otherwise I suggest no other schooling fish as these tend to stress out the girls quite a bit. So the other options would be cory's, always a favorite among sororities since the girls and cories don't share the same space which means neither will stress out the other, making for a very happy tank.
I like to use these: http://www.homedepot.com/p/Commercia...1#.UbXvOOc3szY
if you do not have a hood. Otherwise you can use the hood that came with it and use fluorescent bulbs/tubes. You want to find 6,500 or 6,700K bulbs/tubes to fit them as that will give you the best lighting options to grow your plants.