Ive always used basic stock lighting with my tanks and never had any trouble growing most basic low light plants. You simply have to choose plants suited to that light, and there are many easy basic ones that require very little. I don't add any sort of ferts to mine and it's been going 7 years. Here it is currently
The only thing I have in mine is a layer of pond soil under the sand, but since your tank is already running it would be lot of hassle to re-set up so I'd say don't bother with it .
My plants change around pretty frequently as I often give cuttings and offshoots to my friends, brother and nephewwhen I have excess or fancy a change.
You should have a good layer of mulm in your gravel by now, which should get plants off to a good start.
Easy plants to start with include
Cabomba - easy
Elodia - easy
Aponogenton - long and tall, will fill plenty of space when mature
Cryptocoryne - easy
Echinodorus - easy
Java moss - easy, and tie it to your wood or rocks as it does not root in substrate
Moss balls - easiest plant in existance, just drop them in and leave them.
Java fern - easy , and tie to wood or rock same as java moss
If you get some nice long branchy pieces of bogwood, then tie java moss all along the length of it, and allow to grow. This will really brighten things up, and fill some visual space.
Aponogentons are tall and best planted along the back and sides.
In front of the Aponogentons you could put the Echinodorus and Cabomba and Elodia, and the Cryptocorynes down at the front to fill the floorspace.