This is awesome, wish we had an update.
The "14hp equivalent"... of course that was picked to substitute for the original engine. But this is a single-shaft motor, so you can't use the front PTO on it. Now Case gave us 14hp to both push it along and spin the blades, which are generally accepted to be the biggest power hog accessory, and (somebody can correct me on this) actually exceeds the ground drive on flat and nearly flat ground.
Where I'm going with this: It's another $200, but if somebody wants to do something like this I'd think about getting two 5kw motors, one for the tractor drive and one for the mower deck or (maybe and??) to drive a second hydraulic pump for the tiller. And although it's a bit more for the complete project, you can save about $400 initially and have something you can at least tool around your yard with a trailer and impress your sig other!
Other thought: As far as direct electric drive, actually that's a better "in general" idea but it won't fit and even if it did, you'd be way way better off getting a classic Cub/Bolens/Wheelhorse and doing a pure motor swap.
Final thought: The electric "neutral start" switch can be wired to another relay to invert it, and then it could shut off the motor in the center position.