Im not a fan of DBA (I prefer Warmaster), but the fantasy version (Hordes of the things) is fantastic.
DBA requires 12 "elements" per army.
Using 15mm figures, an element would propably be 4-6 figures at the most, so we're talking 70 figures or so. More if you go 10 or 6mm.
DBA is highly abstracted, and sometimes feels a bit more like wargame chess. But it works out allright, and gives reasonable results, as long as you use historical opponents (100 year war french vs romans will get wonky)
As for comparisons, Warhammer is pretty okay, but suffers from buckets of dice syndrome. Comparisons to 40K 3/4th edition are hard to make, as DBA qualifies as a wargame (though an abstract one), while 40K's current incarnation qualifies as glossy toilet paper