Rico Loma

Many others here with superior electrical knowledge......well, could also be true on a preteen Taylor Swift website.....but you could try a new switch. I see them for 40 usd at Lowes, less at the feed store and discount center nearby.  Last year I had to replace mine (well pump) after some intense days of lightning storms.  It looked fine but often malfunctioned.  You have a new pump but how old is your switch?
And it may be a hassle, but please look at the pump itself.  Being low enough to withstand freezing puts it in more contact with slime, goo, algae, and other wonderful things.  Then you can decide if the screen on the pump is adequate for the task.  

Ned, forgive me if you already considered this idea......a friend used one of these for a year while build his off grid cabin , then sold it for a hefty profit.  

His plan had that extra benefit of time.  Over many weekends he built the " foamy" , made it with attention to detail, before moving out to his remote land.  Once it was parked, he was free to use his truck, unencumbered. That plan might suit you.  

Your location please? Do you have hard freezing of lake for months at a time?
I apologize for asking now, but I'm curious, did you originally consider the simplicity of a DC pump?

Hi Daniel
Try the ideas from William, spot on for your situation ฝ
Forgive  me for being repetitive, but I think you will be happier with a smaller walipini for 2026.  If it works for you swimmingly,   maybe expand the following winter, Nature as our teacher

Nancy, I am green with envy, a Range Rover,  a lovely UK gem.  Hope it's back to you soon.  

Thomas, yes the best oil for you is affordable and highly rated, about 5.40$ per quart.  But could I ask about that mandatory " x miles or one year" we hear from every brand? Your opinion? I do live on a dirt road with no county or state maintenance,  but my oil changes are normal.....never blackened but actually off color amber.  
So I might go a full 10k miles this time, chaged oil 600 miles back, to understand this degradation fully (7 yr old Honda fit , 40k miles, now getting 46mpg city/ highway)
Any other opinions welcome, thanks y'all.

My plea to all car owners is simple, always buy in bulk. The 5 quart size is best, and is currently less than $6 per quart for Quaker State, Pennzoil, Castrol, Mobil 1, and  Valvoline to name a few.  

Thomas
I had to buy paint, milk, bacon, and a new file today,,,,,, of course I stopped by the Mart of Wal.
Had a walk down the aisle with motor oil, and no full synthetic oil was over 26 bucks per 5 quart container.

Are some folks really paying 10 per quart??  Jesus wept...

Back to the OP, please
1. Is this your first greenhouse build?
2. If so, could I suggest starting with a modest greenhouse to grow peppers, tomatoes, chard ......and observe your results over a full year?
    When you're sure about that success, perhaps try tropical trees the following winter?   This might be a realistic two phase solution.

Good plan, Ian,  and I concur with Jay on the daytime playpen.  In my experience with chicken tractors, about two decades, the daytime tractor relieves a lot of worry over predation.  We have nesting hawks on our land, with the voracious opossums,  skunks, raccoons, foxes, coyotes and most recently feral coy-dogs.  

Your average 8 by 4 by 4 is light and easy to start.  Of course your custom bed size may be preferred. This is for hens under three or four. I usually allow hens over three years to free range or live in a tractor, while younger ones get maximum protection  
Older birds have slowed or stopped laying, and are more predator savvy. They are not expendable, but I only shed crocodile tears if they depart for that  big coop in the sky.  
Ian, you don't have to waste space with that tractor, use it in spring as a mini greenhouse, using plastic perhaps, or in summer with branches, leaves to partially shade collards and kale.  Some folks buy shade cloth for their summers.  Best of fortune to you, Rico

In brief, I don't believe a builder can look at a two year old structure and generalize on its merits.  When in doubt, prepare for the worst, that's my maxim.

For example, I am technically safe from earthquake damage in GA.  But what about the NewMadrid Fault? A shift near Memphis 120 years ago famously had church bells involuntarily ringing in Charleston SC.  Look at the distance here.  It is past due for another 6 plus temblor........add in climate change, and
Who knows what stresses await your diy structure?