You haven't mentioned a word about checking the very vessel that will be carrying you. Good battery, engine serviced and oil topped off, all gauges operational, bilge plug installed, do bilge pump(s) work, do the engine bay blowers work, general visual inspection of engine bay, boat exterior and trailer. Trailer tires properly inflated, do the brakes work (if equipped) and are all lights operational. Before you leave the dock, check instruments for proper readings. If one is not operational or reading abnormally, don't leave the dock until/unless you verify why. If the seller says it's a bad gauge, it likely is not and you need to verify what's wrong. If you have little to zero mechanical/electrical skills, then basic tools are of no use to you and a Tow Policy becomes the safety net. Otherwise having some basic tools can save you a tow and save what may be a nice day on the water.