I'd just use three fans and one vent, depends on how tight a fit the hood is.

You can use all four for fans if the hood is loose.
Otherwise the 2 at either end as vents and two fans in the middle will work.

You can buy reflector material for retrofit MH's for a dIY project. Just curve and screw it in how you light.

250w is a lot of light, see if you can sell off this and use 150-175 w instead and maybe add a pair of 2x 96W PC from A&H.

Run the PC for 10 hours, the 250's for 4 midday.

Regards,
Tom Barr