I use 2 koralia #3 for my 75g, in addition to my 1100gph return pump, it's nearly too much water flow. With a tank your sized, I'd probably do a 2400gph return pump with 4 koralia #3
You'll want a pair of skimmer boxes, I used these and they are easy to install and work great. However they come with a glass drill bit, and you'll need a wood bit, I'm sure you could call the owner and tell him what you'll need and he'll hook you up, probably be cheaper as well. TX Holey Rocks
As far as your sump goes, it's really a must, and I wouldn't consider you tank finished or even that it can hold water until you have your sump build and tested as well.
It's not completely necessary to have baffels, I have a 35g sump with no baffels and a 39g refugium. However if you built your sump from plywood, it would be extremely easy to build it with baffels, something simple, like 1 small section for the drop-in and skimmer, 1 large section for refugium, 1 small section for the return pump. Sump's main purpose is to hide your skimmer(and other equipment), act as a refugium and increase water volume. imo