FOSS gamedev and creative worlds

I'd just like to know, because it seems like there are about 7 times more people on the forums than there are playing the game, which makes me wonder if there are servers invisible to me.

No, you can see all of the publicly announced serves at servers.minetest.net.
Not everyone is always on. Some times of the day are better if you want a lot of players.
However more players means more lag.

If you are like me, i check out the forums, then play the game and ill be here for like 20 minutes.

The mods used are dictated by the server, not by your client. Your client always downloads the mods it needs from the server you connect to in order to be able to run a game.