First thing i'd like to say is that i love getting on servers but im only aloud to get on one ounce a month
i just thought id say that beacause i would love to get on servers alot more!
I don't know exactly how much, but minetest doesn't use much internet, much less than minecraft. The biggest download is the first connection when it downloads all the textures, but that is cached so it doesn't need to be re-downloaded again.