The burnt malt must be varying degrees of crystals.. as it is the only malt I know of that would be available both at 50 and 150 EBC with the same trade name, only the color changing..
I'd guess to say the Black malt is just that: Black malt (aka, Black patent malt).
If you buy 1 sack of base malt, and 2 specialties, you will run out of base malt way too quick and have a ton of leftover specialty malts. Base malt accounts for the vast majority of your grain bill...
I would probably get only the base malt and try to find another supplier for smaller qties of specialty malts, or attempt to make my own specialty malt from the base malt.. 100 Kilos of crystal is an incredibly large amount, I haven't use nearly as much in 7 years of brewing, and I brew quite often..
And you can make all kind of beers without specialty malts anyway..