Battery charging takes time and you can't push it. Think like 8 hours of time.
Spare batteries are nice but if you hook them all up together, you'll gain an extra 15% capacity or so due to the Peukert effect
Batteries age faster the longer they sit around at less than full charge. They also age faster if they are run down too fast too often.
What seems to work best for long term off grid is the use of a genset for an hour or two in the morning to bring up the batteries followed by solar panels to top off the charge during the day. If use is low and sun is good, the genset may not be needed.
A tow vehicle should only be used to charge batteries when on the road or in an emergency situation. It is neither good for the engine nor very fuel efficient to let it idle for an hour or two trying to charge a battery.
Solar alone can be a problem in that it can be too gentle on the batteries. They need an appropriate amount of 'exercise' to inhibit sulfation buildup.