@CBDEMON
XM-L2 U2 4C is a 4300-4500K emmiter so when using for veg only you won't have to add any other wavelengths. I would shoot for even higher CCT like 5000-5700K 3C, 3B, 2A and 2D bins.
As you see there isn't much difference between 5000K and 5700K. You have mainly blue spectrum with addition with some red which would be fine for veg only without supplementing any other vawelengths. Blue peaks at 455nm and you have nearly flat curve from 550nm to 610nm where it starts dropping. In case you want to bump reds I'd get me some 2700-3000K XM-L2s like every fourth emmiter. This makes wiring much much easier because the voltage drop and current don't change this way.
Heatsinking: depends on number of emmiters and drive current. Since XM-L2 is a 10W LED you can drive it anywhere between 0-15W (0 is in theory only) . If you're looking for a let's say 150W unit you could go with 15 LEDs driven at 3A but that would mean they would produce much more heat than those driven at 1.5A. So double the count and split the current in half. This way you'll get much higher efficiency (130lm/W instead of 100lm/W) and way less heat. This does double the costs but the life cycle of your LEDs will be extended to the point that they will actually run with 70% of initial output after 50k hours.
You could go with passive cooling and source heatsinks with larger spacing between the ribs like say extrusion in length of 3ft, 3" wide and 2" high. Take 2 of those and spread LEDs equally maybe even four to get even better coverage ( don't know the footprint of your veg area). Again that bumps up initial costs rapidly BUT keep in mind you won't have to touch that unit for the nex 5-7years at least if done right. On the other hand you could take thinner lighter extrusions say 1" high and add vents. This will give you lighter unit but adding the complexity of the build, needing another power supply for the vents (unless running of mains).
When it comes to cooling make sure you use quality products in form of thermal paste/glue, flatten out contact surface as much as possible ( LED and heatsink) and make no mistakes.
Drivers:
Meanwell! The model depends on your choice of emitters, count and power.
You could also go for COBs which would bring down the complexity but the costs wouldn't change much except for the heatsinks. You could use CPU heatsinks in this case or make a unit similar to the one you're referring all depending on the power used.
Hope this helps a bit. If you have any question just shoot them at me. It would be much easier to talk about certain build if I knew some numbers like footprint and power.
Keep it green!