Is is very possible. It is also possible that using the same bottom bracket (spindle) will result in the chainrings hitting/rubbing the chainstay, so you may need to get a bottom bracket with a longer spindle.
I never learned to ride a bike. It is my deepest shame.
Yes. Possible. Standard road cranks with a 130mm bolt circle diamter (BCD) will give you awfully tall gears for mtn riding. The newer 110mm BCD 'compact' cranks use the same chainrings as outer and middle mtn cranks from years ago.
Also, the chainline might be a couple mm off, but probably to no great consequence.
General questions get general advice. Of course it's possible(so is flying to the moon BTW), but the degree to which it works depends on the frame clearance for the chainrings and arms, so choice of crank matters.