It makes no difference to the function of the HW Htr. wether or not the valve is open or closed.

What does make a difference, is if the power is still on. It should be off.

When you have the repairs accomplished, open all the valves on all the fixtures. Then open the main valve slightly until you hear water flow. Starting on the hose bibs and the first floor, If you have single handle faucets, alternately switch from hot to cold until the water flows consistently, then shut the valve off. Continue until all are bled and off, then open the main all the way and turn the power back on to the water heater.

It is good practice to shut off the heat supply to the water heater if the water supply is off- especially if the heater is electric. There is more than one potential way that a non-pressurized heater can drain at least part of the water. If the heater element in an electric heater is powered when dry, it will burn out the element very quickly.

Great, thanks!
Now, if I could just find the darn breaker...I turned off one that said "water pump" but the ac went warm ooops.

What about before I have my repairs accomplished, do I have to open all the valves and bleed as you described, each time I turn the water back on to test while I "leak detect"?

Not necessarily, just be careful not to turn the water on full pressure, just enough to pressurize.

Great, thanks!
The main has a ball joint valve just like on top of the water heater i.e. "open" or "close". That said, should I still be able to find somewhere in between full "open" & "close" in order to not to turn the water on full pressure?

"should I still be able to find somewhere in between full "open" & "close" in order to not to turn the water on full pressure?"

Sure, just barely crack the valve and listen to it squeal. But your question is a good one as it is in fact difficult to 'throttle' with a ball valve.

Great, thanks!
Hopefully this is not a stupid question...but would I be doing any damage to anything by filling the toilet tank with rain water to flush the toilet, while the main is closed?

A better system would be a bucket of water available, or a "thunder mug" by the back door.

would I be doing any damage to anything by filling the toilet tank with rain water to flush the toilet,?

Not at all.

Great, thanks!

Turning on the water and trying to pressurize was kind of like finding the sweet spot while driving a clutch...but eventually got it...just had to be patient. Now, if I can find the darn breaker on the hot water heater end the stupid leak itself.

Yep, being patient is a virtue.

Short of identifying a specific breaker, you can shut the main off.

Or, hire someone to remove the dead front panel on the service, because there may have been some "entrepreneurial" wiring going on where they have tapped into several breaker feeds for the power to the hot water heater.