I've begun my brackish plant project, to try to give my puffers some real plants instead of those cheesy plastic ones

It probably wouldn't be such a big deal except that I do
not have a green thumb. I'm struggling to keep my plants alive in freshwater, lol.
Some background: my 20 gallon brackish tank came with a full hood with a 15W fixture. It's home to two little green spotted puffers, and the tank will be upgraded to at least a 55 later, and used for a single
figure 8 puffer when that time comes.
So here's my progress so far:
I got a glass top to replace the hood.
I got a double fixture that supports two 20W bulbs at Home Depot.
I took out a bit of my hornwort that wasn't doing so hot from my
betta tank, and put it in a bucket. I'm slowly adding in some water from the brackish tank to
acclimate the plant to the
salinity. I figure that since the plant was gonna die soon anyways, might as well use it as my test run.
My to do list:
Get some sheet aluminum to make "legs" for the light fixture to stand on.
Get more plants (quite excited about this one, although it won't be for a while)
Make a CO2 system. I've found quite a few ways to do this on this site and others. Does anyone have any experience on which is the best?