That is a good RPM range for outboards. The charging depends on the brand and generator/alternator on the motor, they will vary. Trolling with a single engine is good but make sure to offset the hours from trip to trip. Oil injection is nice but stick without it and mix your own untill you get new motors. Keep life simple on yourself. It is unfortunate that you cant plane on one engine, that is kinda the purpose of having the twins, being able to cruise in if something happens to one engine. But oh well, cruise it in. Better than drifting. Best bet for RPMs and amp charges is look it up online.