Thanks for your feedback guys!
Yesterday it was bright out and the light looked pretty good, today it's dark and rainy and I can see that it's probably not going to cut it. Bummer. So I'll be upgrading that pretty soon. Would y'all really recommend the 24" over the 20"?
And thanks for the list of potential plants Russel, I am so bad at keeping track of plant names! I think it was Crypts I was thinking of, but my fingers decided to go with the Amazon Sword. :)
As for the substrate, hmm. I used ten pounds of sand, so I was pretty sure that would be enough. I will keep an eye on it and see if I need to get some more, or possibly even switch it out completely for dirt + sand, which I almost went with but decided against at the last minute to keep things simple.