The 50W should work fine in terms of the power, but I would take a closer look at the spectrum. These lamps are usually designed for outdoor floodlights so you will not get much red past 650 nanometers. Could be a problem for flowering.
This is most likely fungus gnat larvae. I had them in my setup as well, and noticed a lot of gnats flying around at the same time. Gradually died off after diligently removing them from roots every couple of days. Definitely not worms. See here.