I use connectors with 4-5m of 14AWG double insulated wire. I'm not sure if you have a tent, but Airwalker is right about the connectors making it easier to run wires in and out.
I've always run my lights at night. Over the years I've tried running them during the day in winter to see if it makes any difference, but found the lower overnight temps retarded growth more than the added warmth during the day accelerated it. So I simply aim to keep my grow area reasonably warm at all times during winter, and reasonably cool during summer (no easy task with overnight temps in the high 30s).
If you run remote drivers, then you have the option of moving them inside or out depending on time of year. Regardless, the cooler you keep your LEDs, the more efficient they will run. So if you want more warmth in the room to help with growth, the the best place for the drivers is somewhere near a fan that will mix the warm air. The LEDs themselves will also produce heat, but you don't want to add heat to them with the drivers.
600W of LED will generate a similar amount of heat to 600W of HPS, but the HPS heat will be more concentrated. The advantage of LEDs is they will generate more usable light for the same power draw (also, LED light always points in one direction - HPS light is usually reflected, making it less efficient - unless you grow vertically), so you can either grow more plants (more yield) with the same 600W, or turn the LEDs down to 400W or so to produce similar yields to the 600W HPS with less generated heat.
There's a bit of a debate about "heat vs light" in one of the other threads here that I've waded into. Simply put, light is thermal energy, and any time energy is transferred, it is in the form of "heat". Light reflects off other objects (which is why we can see them), but is slowly absorbed as it continues to reflect and refract. If it reflects off an object (mirror, reflector), or passes through it (glass, air), or is diffused, then it does not transfer much of its energy to that object - the temperature does not rise by much - and will continue to bounce and reflect off other objects until it is all absorbed (with a corresponding rise in temperature over all those objects).
Thermal energy can also be transferred directly - that is, "heat" (as we typically know it) being conducted from one object to another by coming into contact with it. Metals conduct heat very efficiently - that's why they get hot! Air also conducts heat, but not as efficiently - that's why a metal object will heat up a metal surface next to it, and to a lesser extent, the air around it.
What I'm trying to say is, it seems counter-intuitive that 600W of LED will produce the same "heat" as 600W of HPS, but they just produce that heat in different ways. Some of the heat (light energy) gets bounced around and absorbed by plants and converted into stored energy (sugars and starches). Some of the heat (conductive energy) is absorbed by metal and other fixtures and the surrounding air directly from the element itself (HPS bulb, ballast etc). Some of the heat circulates around the room in the form of hot air (convective energy), heating up other things it comes into contact with.
In a sealed environment, eventually everything heats up to the same temperature, and thus all the energy in the environment returns to a state of equilibrium.
All you need to know is the more energy that can be converted to usable energy by the plant in the form of PAR (photosynthetically active radiation), the less total energy (heat) you need to introduce to the environment to get the same results. That is the advantage of LEDs. The other is they produce less conductive heat than other light sources due to their efficiency and smaller size for the same light output. So they are "cooler" to the touch and do not concentrate heat as much in one spot as a HID element.
Hope that all makes sense
but I want it to easy for the missus (yeah I know she should be able to look at the power meter, and as you mentioned once I get the hang of it it will prolly only change from seedling stage, veg stage and then full power.
