How big is the tank? If it's less than 100 gallons, a LifeReef single overflow would be plenty. It should flow at about 700 gph. I think that's about the rating for the LF 125 anyway. I'd use the Ampmaster for a closed loop, since you're not going to be able to get nearly 3000 GPH from any overflow. There are a few plumbing nightmares with trying to get that much flow through any closed loop system, but it can be done. Maybe Pro-Builder cann offer some tips for bending PVC to make a suction tube that will work. You'd need 1 1/2" PVC in order to get anywhere close to enough to feed that pump.
I'd use something like a Mag 7 or 9.5 for the return pump from the sump. Does this come with the pump for the skimmer? See LifeReef for recommendations if not. You should stay with the pumps Jeff recommends, as they are what he tests the equipment with, and will probide you with the maximum efficiency for your skimmer.
What a sweet deal. I was looking at pretty much the same Lifereef set up a couple of months ago, without the Ampmaster, and the asking price was $500. + shipping.