I may do cryptocoryne wendtii. It both looks best and would do best in my low light tank. Though wattage is good @ 17w/10 gallons, it’s a tall tank, not wide. My tank is about 15 inches wide, 18 tall, and curves in the front. It’s a rather odd tank, but it’s even harder to light.
I have no idea about wats per gallon that's normally reserved for fluro tubes. I work in Lumens and Kelvin
This tank has a BEAMSWORK Hi-Lumen 60 (180cm) (Planted) 3 times as long as the 2 footer and 3 times the price. The light is 3 years old and still works great
If you want to experiment with different degrees of darkness try rooibos tea if its available where you are - its dirt cheap. Don't be taken in by the "organic" marketing tricks. The plant is so sensitive that the only way to grow it is organic so just use the cheap stuff.
I'm in the UK and my local supermarket only has one type. I throw a few bags into a jug of boiling water on the morning of water change. Then sqeeze them and put the water in the tank. 4 bags gives a nice rich colour (but not too dark) in a 180 litre tank, then adjust to taste for subsequent changes. I know some people just put the bags, or loose leaves in the tank or filter.