The oil add tube should be a yellow plastic cap. BUT. DP dipsticks are notoriously in accurate from the factory. The procedure is to check with CAT to establish how many qts it takes. My CAT uses 19. Get it changed and then on level ground, establish where the oil level is on the dipstick. If the existing one is ok you are lucky. If not use a file to make a new one.
Next did he keep all the maintenance complete? At 5 years ALL fluids; coolant rear end power steering transmission engine and filters. Trans engine air system desiccant.
$2-3k. This goes for genset too.
Tires how old? If factory they need replaced IMHO.
I would use T105 batteries and replace the jack.
Buy a Pro Fill water system for the golf cart batteries.
WELCOME TO DP WORLD.