If you've got a good price on minis you like, then go for it
As far as that set in game, it seems pretty solid to start with. Good mix of shooting + fighting, with decent synergies provided by the Fleetmaster (+ Corsairs) and the size of the Darkshards. You'll probably want to pick up a heavy hitter next - Executioners are among the best troops in the game and should definitely dish out some hurt, though a Monster and a Wizard wouldn't be bad ideas in the near future as well, because Cool and Good and all that.
As for balancing your armies, I would heartily recommend considering the SCGT pool system, it's been good to me in my recent games, and certainly better than just going by wounds (and infinitely better than models). Under SCGT this warhost box is 35 choices, with 5 Corsairs that you'll probably want to find somewhere, as virtually all pool systems work in multiples of warscroll minimum unit sizes (so 10, then 20, then 30 for Corsairs, while the set comes with just 15?). Anyway, the SCGT itself ran at 100 pool choices, with a total pool of 150 to choose from, but you're welcome to dial it down as small as you like. 50 with 75 pool would be closer to a 1000 point 8E game if we consider 100 pool a 2000 point game. (Making 35 around 700 points.)
SCGT (and more) builders can be found here:
http://scrollbuilder.com/ But yea, get the set, then add more cool things
- Salvage