DSD calls them "filendunun." (Looks like that's singular, not plural.)
The mallets are from DSD - they normally sell a pair with the water drum, but somehow, one of the mallets for the one I bought went missing and they sold the whole megillah for 1/2 price. I'm not quite sure what they used to pad the mallets, but they're pretty heavy.
As far as the amount of water in the drum, I'd assume that it all depends on the pitch you want to get. So yeah, just enough to float the top calabash is one thing, but actual tuning is another. I'd ultimately like to get a couple more of these (in different sizes) and have a set.
Thanks much for the tip on beeswax - my only concern is how easily the calabash absorbs it, and whether it will melt in our humid summer weather. (Our climate might be called "temperate," but that's a real misnomer!

It's one thing to keep instruments in an air-conditioned room, but a whole different ballgame when using them in performance situations with no a/c, 80-96 F heat with high humidity....)
they have surprising sound projection...
Yes- I wasn't expecting that and it was a real surprise!