125 gallon mixed reef triton method build help

Hello,
I am new to the forums but have been keeping reef tanks/fowlr tanks for the past five years. I recently picked up a 125 gallon tank that was brand new from craigslist for $100 dollars so that was too good of a deal to pass up. So, since I have picked up this tank, I was looking to see what everyone thought of my current plans for setting it up, plans are as follows:

• 125 gallon display tank
• 75 gallon sump/refugium
• currently I have about 20lb of live rock, and about an additional 70 lb of base rock from my 75 gallon FO set up. So 90lb total, thinking another 30ish pounds? I like open areas for fish to swim
• Thinking mixed reef for the coral selection
• I want to keep active fish so the tank seems fuller than it actually is.
• Triton method would be the goal for this set up, hopefully a 75 gallon sump is large enough to achieve this.

Feedback on those things would be appreciated as that is what I have kind of set my mind on as for now, and would like to see what people think of it and see if it is in fact something that someone could achieve.
Some other things that I would need to consider but do not know where to start are:

• Lighting, I have run Kessil pendant lighting in my tanks and I have run t5ho on my tanks, I really like the kessil lighting but I dont know how practical it is to use these lights on a 125 gallon due to the length. My current thoughts would be metal halides (maybe, I know these get hot, but I live in ND and this would be in the lower level of my house), with some retrofit t5ho bulbs put in, along with some moonlight led lights for the night time effect.
• Stand, the aquarium that I had picked up did not come with a stand unfortunately, but it was 100 dollars and it still has the box and stickers on it so it is brand new. What would be the best design for a stand, I want one that is tall enough and deep enough for my sump (75 gallon) to fit underneath. Also I would like to build it so the height of this aquarium is right around 36 to 40" off the ground. This being said what are some stand designs that other people have had success with.
• Overflow, I would like to drill this tank, but I really do not want to mess it up, so how effective are the hang on back overflows that I see on the internet for sale. Are they effective, I have seen a lot about them siphoning too much water into the sump if the power goes out. So what would be the recommendation to drill or not to drill?

Just really excited to have something bigger than a biocube sometime soon.