With pull start and electric you pretty well have the basis covered. A synthetic oil for sure and a battery pack, maybe a can of starting fluid. Make sure that pull rope is in good shape. I would think just out for a day of fishing and letting it idle every once in a while would be good. Seems like sitting over night is what get’s everything all tight and even a pull start is a PITA.
Pretty sure there are 12 volt oil pan heaters, wolverine is one company