VEVOR 3/4" PEX Tubing 500Ft Non-Barrier PEX Pipe Blue Pex-b Tube Coil for Hot and Cold Water Plumbing Open Loop Radiant Floor Heating System PEX Tubing (3/4" Non-Barrier, 500Ft/Blue)

This stuff can freeze solid when full of water and won't break, so yes, you can use it above or below ground.

I see no reason you couldn't

Probably ok if under just a few inches and with no stones but I would not use it in ground, unless you put it into a sleeve. We have sleeved pex inground but not long enough ago to know how it will do.

Yes, This should work well for your supply line from the well pump to your house.

Yes it definitely will. Be sure to protect the pipe with a sleeve or insulation when it's buried.

I would say that you would need more volume than just a three-quarter pipe