100A subpanel to workshop
For the sub panel sometimes you can get a better deal on a 150 amp panel your panel really cannot be two large.
Yes you will need a 4 wire feed but your main panel will dictate the size feeder wires , if I was doing this and could get a 125a breaker to feed my shop I would do it, however many panels will max out at 100 amp so size your feeder wiring on the size of your breaker.
The size of the sub panel is not the controlling factor it’s the breaker in the main that feeds the sub your sub has to be at least that big but going bigger is usually considered better.
Large feeders , most pros will pull aluminum no worry about voltage drop here and with large conductors conduit and individual conductors are the way to go the ground wire will be much smaller based on the size, yes the other conductors are based on size but grounds are a different table.
You also need a local grounding rod for the sub.
So go big on the sub panel even If you only want 80 amps, use conduit PVC is easy to cut and glue schedule 80 above ground 40 below ground,
IF you use a smaller wire size do your self a favor and over size your conduit 1-1/4” or 1-1/2” will make an easier pull with large aluminum and if you decide to go max size later it make using the existing conduit possible and a later upgrade simple.
Newer code mandates all receptacles to be GFCI protected.