What wattage for 2 gallon NPT

I have a 2 gallon aquarium I am going to be setting up as an NPT (natural planted tank) housing red cherry shrimp - I know the most important factor in setting up an NPT is getting the correct lighting.

I understand lumens, kelvin and such but I am at a loss as to what wattage the bulb should be. I have been looking at aquatic plants all day trying to decide which ones I am going to order in the hope that this would help me understand what wattage I need but it unfortunately has not.

I have a 25watt CFL (colour spectrum 6500k) and appropriate lamp that I was going to use but I am concerned that this will be too powerful for a 2 gallon aquarium. I have searched for lower wattages and initially wanted a 15watt CFL but the only 15watt bulbs I can get have to be bought in bulk - and it isn't cheap. I've also spotted 11watt CFL 6500k bulbs but I do not know if these will be powerful enough. I've done research but can't for the life of me get to grips with what wattage I need.

As mentioned I am unsure of the species of plants I'm going to be using in the aquarium but am looking at the following:

Hygrophila Difformis (Water Wisteria)
Echinodorus tenellus (Pygmy Chain Sword)
Willow Moss
Water lettuce
Round pellia

I have a feeling I'll need more species, but the above are just some of the ones I've looked at today and quite like. My head is beginning to hurt. Any advice would be GREATLY appreciated.

Thank you.