Welcome to the club Larry! You have come to the right place. I'm no expert, but certainly willing to add to the discussion where I can.

Regarding question #3...Your looking at about a half million gallons according to...

https://www.gardenponds.com/Rectangular-Pond-Calculator.html

Take a five gallon bucket and fill it up from your spigot and time it to get the flow rate. I can fill a bucket in about 1 minute with my small well system...[500,000 gallons of pond water/5 gallons per minute (my flow rate, yours may vary )/60 minutes per hour/ 24 hours per day] yields about 70 days to fill your pond with a garden hose without any help from mother nature. If your pump goes out during the process, it was on it's last leg anyway, OR the water level may have dropped below the suction of the pump and burned it up. It's a craps shoot (with betters odds that nothing bad will happen).

Will the pond have any watershed? If not, you will likely be topping it of on a regular basis with well water anyhow. If it does, mother nature will fill it (eventually). Make sure you do not have too much watershed or it shortens the life of the pond by filling it up with washed in sediments and can lead to erosion issues over the dam.

I'm guessing the high iron will not bother your pond any and I don't believe it bothers fish either, but I look forward to the experts responses on this one (and the other questions as well).

Good to have you!

Fish on!,
Noel