Will have to change thread title as i have decided on a reefer 425xl
Hydra lights, vortech qd pumps, red sea skimmer
Do I go for 2 hydra 52, 2 hydra 26 or 3 hydra 26?
Do I go for 2 mp10's or 1 mp40?
Do I go for a red sea skimmer 600 or 900?
Do I go for a Vectra small, medium or large return pump?
This applies to most LED fixtures like the Hyrda 26, Hydra 52, Radion and similar point source LED lighting.
Generally you can figure a LED fixture like that is going to cover about 2 foot (60 cm) square on a tank. A Reefer XL 425 is about 47 inches, almost 4 feet long (120 cm) so you'd want to see 2 Hydra 26 fixtures as a minimum. However, depending on what your keeping in the tank, and how much light you want, you could go with two Hydra 52. That's a ton of light though, and you'd need to be very careful with them, since it's easy to "burn" new corals or have bad algae issues. If I were setting this up, I'd go with 2 Hydra 26 fixtures. That should work fine for you. Later on if you feel you need more light you could add a 3rd fixture.
When you rate a skimmer for a tank, you tank the the manufacturers rating for the tank size it can handle and use that skimmer on a tank about half that size. Manufacturers tend to ve very "optimistic" about the size tank the skimmer will support. In your case the 600 is rated for an SPS tank of 160 gal (600 l), so you should be fine with that.
When you size a pump, figure you want to turn over the tank volume about 10 - 15 times an hour, so the Vectra S1 would work fine if you just want to run the filtration system. However a lot of people T off the main pump return and run part of the water through various reactors, UV or a refugium. The nice thing about DC controllable pumps is that you can easily dial them back a bit. So you might want to get the Vectra M1 if you think adding reactors or other equipment is in your future. Note - you sometimes see people talking about a flow rate in their tank of 30 times an hour or even more. There people are almost always adding on the flow pumps they have added to the system. You may want flow pumps, but that's something different from the main return pump.