The elements are in.

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Those were much more difficult to install than anticipated.  The threads are tight, the rods go far into the tank, gravity is difficult to assuage.  Still, after a bit of practice, then doing the top one first (to make sure which way to even twist them in, as that ended up being easier for a number of reasons), I finally figured things out, got it in, the got the bottom one in.

To tighten without breaking, or leaving any sort of gap by which water may spray out.  A bit of a trick.  I think I did it.  I got them snugged, right up to where there was no more give... no more room to tighten.  I hope.  But, that... wore me out again.  Back to gaming for a bit.

And, to consider what to do next?  Either redo the electronics, then turn on the water.  Or turn on the water before tinkering with electronics?  I think I will turn on the water first.  If it sprays the old electronics, that won't be as much of a problem.  Those parts are being replaced anyway.  But, if the new parts got wet, getting them dry, for certain, might be a bit more difficult.  I will go down and put the new parts somewhere safe.  Maybe bag them and bring them upstairs, just to be extra careful.  Then, make sure the drain valve is shut, tight.  As well, I will open a few of the hot water faucets around the house.  Just... not in the bathroom.  That one is too likely too flood.

Then, out to turn on the water at the main.  And, check various things.  If it works, I will turn off the hot, then turn on the cold, faucets in order to pressurize the whole system.  If it gets wet, then I'll... have to sort that out, sometime in a bit.  I would have to turn off the mains water, again, and... just pout for a bit.  Then... tighten things up.  Actually, I would try to tighten things then and there.  I wouldn't turn off the outside water unless I couldn't close the leaks.  Bleh.

Why all this chatter?  Making plans, creating a decision making tree, being mentally prepared for good, worse, worst.  If all else fails, there is another option, if I'm not sure I can do it solo... installing the spare water heater.  Everything should work on that, and most of it, save emptying and moving the old out, and the new in, is rather straightforward... if only ever done once before.  I did that solo, but was ten years younger.  Bleh.

Well... I may just do the water, right now.  Uhrm, after bringing the parts up, opening a few valves, ensuring the drain valve is shut, and... I think that is it.  Well, and maybe checking the elements one more time.  A quick solid jerk at tightening, just... to try to be more certain.  Later.

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So far, so good.  Dry where it should be.  Taking a while to fill, so I turned off the faucets.  For the time being I will just let the tank fill.  I am sure, by the time I checked, the bottom element was submersed.  Not the top one.  Getting there.  If all goes well, stays dry, then I can begin sorting the thermostats, getting the new ones installed.  Doing a few checks before even turning the panel back on.  Then checking after.  

Check, test, double check and test.  It's the only way.  Slow, easy, considered... one thing at a time.  Even so, failure is a possibility.