Thanks everyone for replies and all the good info.
Couple notes.
It's probably helpful for newbies like me to keep the discussion as specific to the OP's engine as possible.
There are most likely some differences between the 3.0L and 5.7L engines.
The differences is that the V6/8s have drain plugs on each side of the engine, the 4 cyl I am not sure about, it may have only one...
The V engines also have 2 exhaust manifolds each one has to get drained. Both have raw water intake hoses that should be drained and the big hose on the front water pump needs to be drained on the bottom end for both. For example the one I have has the single point draining system (just houses attached to drains at the bottom side of the engine) but I didn't notice any other draining plugs etc.
Get a hold of a manual if you don't have one to make SURE....I don't know for sure how the single point drain is set up, but there MUST be a drain on the exhaust manifold, it holds a LOT of water. I didn't have time to find and check the water pump on my engine but am planning to do it in Spring.
Are you referring to the raw water impeller (Alpha drive, its in the drive lower unit, that one requires replacement about every 2-3 seasons) or the one on the front of the engine, they last for 20+ years. The thermostat housing does have a gasket which I had to scrape off.
Since I didn't have a replacement one, I didn't put one back in.
I assume it'll be ok without it for the Winter if the boat is not used.
Someone please remind me in Spring (March here) to install one before going out on the water
Actually I plan to clean and sand down a bit the rust inside the thermostat housing since it's looking a bit rough on the inside and might impede flow.
Thanks again