Both will work totally fine together! No problems there.
Not much, really. If you dont prefer the look of Blackwater/Tannins (Google for pic) then, soak it in a bucket of water until the water runs clear. Or just leave it be. It actually helps fish a bit. You can also use carbon in your filter to extract it out.
You say background plant, as a carpet plant. Not sure what you mean. Tall background plants that are easy are:
Water Sprite and Wisteria
Carpeting plants that are short and easy/lowlight are:
Java Moss (Not carpeting but you can make one with tiles. Ask for more info, and I'll provide.)
It depends. If you plan on doing a low tech/lower maintenance tank, you can stick with gravel. If you do so, by all means go for it. You will be limited with your plant choice however. If you go with gravel, use the same fertilizers as the below paragraph.
I recommend, if you choose to go the next step, to buy ecocomplete. It is a planted tank substrate. Along with it, buy Osmocote + Root tabs. I sell some, starting at 120/ $10. Use these every 3-5 square inches. These are stuck in the substrate, 2-3 inches deep. As deep as possible is the point. It provides more nutrients for the plants. If you use these tabs then you should go the whole mile and get lots of rooted plants. Also buy Seachem Flourish and Seachem Flourish Excel. These provide more nutrients and C02 that all plants use. Be careful dosing; be exact. Last buy API Leaf Zone as the last fertilizer. That is my arsenal.
^^ If you want, you dont have to use the root tabs if you go with a better substrate. Its recommended, though.
For lights, a florescent t5 light fixture will be great. 12/24" is good for me. However, regular florescent lights also work for me in my low light tanks. 1-1.5 watts of CFL per gallon is good for a low light tank. As for chemicals, ^^^. Neons are good fish. If you want something unique then maybe go with shrimp. Its all up to you. What type of fish/animal do you think appeals to you? Puffer, frog, shrimp, snails, bettas? Its all really up to you. Food goes after you decide the fish. Down the line there are more advanced tools and chemicals you can buy. But your not there yet and its not necessary yet.
Any other questions, Im here to help!!
For you; a short list of awesome low light plants that are pretty much indestructible:
-Najas Grass/Guppy Grass