[frizzen]

I would definately do a battery Master switch if there's no planned way to actually pull the battery plugs apart.
Your esc even Off will still pull some power and it can eventually destroy cells if left connected.

It'll have like an Off/Charge position and Run position. Wire the Battery + to center leg, esc input + to an outer leg, charge jack + to opposite throw outer leg. Then you can just hook the - wires all together.

The diode to make sure you can't apply power backwards is good practice. However if you're running a connector type that already does polarity protection it's not as much of a requirement. Panel mounting something like Deans or JST that already has an industry standard and can't be connected incorrectly, i'd probably be ok without one. If youre going for Barrel or Ring-Tip kind of jacks, i'd absolutely put in a diode.

Nimh should be good to go for internal charging. Make sure your battery won't get very warm charging at the planned amps before you button it up.