I prefer LEDs because they run cooler, have a smaller chassis, use less energy, you don't have change out the bulbs annually, and some have color control and dimming capabilities. Popular brands include Finnex and Current USA. Many models to choose from.
This link has lots of pics of categorized plants. Helpful when trying to decide on what to get:
http://shop.plantedaquariumscentral.com/Aquarium-Plants-_c_12.html
A 20L is small enough for DIY CO2 IMO. You may want to consider starting out with DIY CO2.
For pressurized CO2 you will need: CO2 tank (regular or paintball size), regulator, check valve, bubble counter, CO2 tubing, CO2 diffuser, and a drop checker.
You will want to consider a decent fertilizer regimen. Depending on the lighting, Seachem Flourish Comprehensive plus API Leaf Zone make a nice combination of micro and macro ferts. Green Leaf Aquariums (GLA) has a few fertilizer packages that frequently used by members on this forum on their planted tanks.
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