Off the top of my head,
Any idea why day length would vary if not for an expanding Earth?
Earth Moon dynamics
Do you accept that there was/is significant radioactive decay producing lots of heat in the Earth’s mantel/core?
Sure, once that cools plate tectonics stops
Do you accept that fission produces little change in mass but significant change in volume/density?
What is "significant." <1%,<10%, >50%. I haven't read anything on that particular aspect of fission byproducts so would appreciate if you could link to something specific I could learn from.
I do know that molten oceanic crust produces granite which takes up more space - which is what makes continental crust lighter thus buoyant and floating on top oceanic crust, but actual volume increase I’d image, just guessing here, <5% increase in volume.
I also know that Earth is constantly being bombarded with way more micrometeorites than previously imagined. But all that is chump changed compared to our Earth’s size.
Have you observed that if we “roll back” the sea floor spreading from the mid-ocean ridges the continents – out to the continental shelves – fit together rather nicely all around a globe roughly 65% of the current diameter?
Sure. Brings us right back to the ring of fire. In the middle there's a oozing suture that's actually spending and at the edges, there are deep ocean trenches that swallow that extra crust in a surprisingly different ways. Well, so far as the what the subducting tongue does, sink or warmup enough to expand enough to become buoyant and start pressing up against the continental crust it was diving under.
Do you have an explanation for how the single super continent – out to the edge of the continental shelves – would have formed several miles higher than the rest of the Earth’s surface 2.5 to 4 billion years ago? And how the parts that broke up from that super continent have maintained their elevation?
There was never "The Single Super Continent" - it was small island arch growing into continents, them nonstop colliding with and careening around each other, then moving on until the next meeting.
Mountain ranges, not entire continents rise up miles above the mean continent.
Himalayas - India. Alps - Africa. Sierra mountains running all the way down the western spin of North and South America - the Pacific Ocean plate. And so on.
Could it be possible that the entire Earth was covered with an ocean for several/many million years when it was smaller in diameter? How about an explanation of how the continents came to be covered with several miles of sediment.
As it happens I’m from the Colorado Plateau perhaps one of the most astounding examples of continental scale subsidence and the accumulation of dozens of thousands of feet worth of sedimentation during the hundreds of millions of years worth of stretching and subsidence, Earth’s tectonics shifted around and started squeezing western part of the American continent, raising the entire plateau and allowing the Colorado River to carve the Grand Canyon, revealing all those layers that used to be buried deep within Earth.
Of course the biggest question is why the mid-ocean ridges are where they are and apparently have not drifted here and there like the continents.
What makes you think that ridge hasn't been shifting? Have you ever read anything stating it's been stable? Please to cite that article - lets have a look at it. I say this because sounds like someone is pulling your leg.
Plate tectonics is probably responsible for some or even most mountain building at the edge of the continents, but it does not appear to be consistent on all the coasts.
This is arm waving. WHAT does not appear consistent on all the coasts?
Identify it and I’ll beat you plate tectonics will help you understand mysteries such as why the West Coast of North and America looks different from their East Coast.
To me, an expanding earth gives more plausible explanations for the Earth as we see it today.
More Plausible? So how much expanding are you imagining? What features does and "expanding Earth" explain that plate tectonic does not. Can you list any?