Unless you have documentation of when the major services were done by the PO, I would advise that you replace all the consumables so that you have a base line of when the maintenance schedule begins. This means all hoses, hose clamps, belts, impellers, water circulating pumps, filters, fluids/lubricants, plugs, wires, distributor cap, rotor, and thermostat. Check for oil leaks and address as needed. Inspect engine mounts front and rear. Parts can appear to be perfectly good and usable but that can be deceiving.
Write on the oil and fuel filters the date and engine hours with a sharpie. If you haven't, get a little log book and write in it all that you do to the engines so you have a record.
Put together a spares kit that includes an extra of everything I listed along with prop nuts, cotter pins, fuses, circuit breakers, and enough oil for a complete change as well as lower unit and trim pump oil. Even if you have no idea which end of the wrench to hold, a rescue boater probably would and maybe find something in your spares kit that will save your day/life.
