Since this is a used, but new to you boat, you would be well advised to pull the outdrive and do full maintenance on everything. Check the oil, any metal in it? Any water in it? Pull the top cap off the drive, is there anything on the bearing races to tell you there's a problem. Inspect and lube the u-joints and gimbal bearing. Any water in the u-joint bellows? Disassemble and inspect or replace the water pump impeller. Look at everything.
Do an engine oil change so you start fresh. Inspect cap, rotor, wires and plugs. Do a compression check on the motor - that will tell you more about the internals than anything else. Pull the fuel filters and turn them upside down in a clear jar - any crap in the fuel to be worried about?
There is nothing worse than having to walk back from a boating trip early on in your boat ownership days. And nothing burns more than an expensive repair that could have been avoided.
Go to the Adults Only section and read up about maintenance items that you need to have some knowledge of. Make sure you follow the OEM Mercruiser Manual when doing maintenance and repairs. Never use a Seloc for anything but leveling your RV or starting fires.