I would go with 10 watts. I don't know about tennelus though. I have 20 watts over a 2.5 g and I only dose Flourish, Potassium, and Excel.
I have pressurized co2 on my 2.5 gallon planted and it does not have that much algae problems. Just planted it like crazy and throw in one or two amano shrimps. Oh and do small water changes weekly or every other week.Dont do CO2... within a week you wont be able to see into the tank b/c of all the algae problems.
Is there something bigger than the nana?... Yes! the anubias coffeefolia is one... here's a tip: just go up to that little google search bar on the top left, and type anubias. There will be hyndreds of varieties that pop up-try it!