The pull elbow is meant for individual wires and won't provide the proper radius for NM cable.
5 times the width (taken at the maximum diameter) of the NM
NM can be used within the structure, without a separate insulated grounding conductor.
Once it leaves the structure it has to have an insulated ground conductor.
The labor calculates to be >$174 an hour.
At least 2 of these tasks could be done by a single man (permit and water heater bond)
Get at least 2 other quotes, for sure.
MC cable doesn't require insulators of any kind. The mylar jacket is enough.
(I contacted tech support at Southwire and they say the attached bag of redhead insulators with every roll was just "extra insurance".)
The only cable that requires them is AC cable because of the paper jacket
What do you intend to plug into the GFI? What ampere rating is the circuit breaker?
I'd be suspicious of tripping the breaker if it is something like a hair dryer.
With single phase circuits, the cable between the meter and the first panel is only 3 wire.
It sounds like the cable you're using is for a 3 phase panel with a reduced neutral.
Ground wires are green or bare, not white