No start after thermostat replacement?

Hello, I'm not sure what went wrong there with the repair, but if the crankshaft won't turn, try removing all the spark plugs and then try turning it over by hand again. Double check that no wires got pinched anywhere when you were putting things back together. If you're able to turn it over with the spark plugs and fuel comes spraying out of one or more of the cylinders, it hydro locked for some reason. Check that your oil doesn't smell like gas as well. What did you have to remove to get to the thermostat? It doesn't look like there is much that needs to be removed for a thermostat replacement.
Did you try rotating the crankshaft by hand?
Is it possible the Starter wire got knocked off when working in that area? It's right near where you were.
Here's the Starter circuit diagram and fuses just in case you need them.

No, a crankshaft position sensor would not prevent you from rotating the engine over by hand. But if the head gasket is leaking into one of the cylinders and filled the cylinder up with coolant, it would hydro lock that cylinder, because you can't compress a liquid. Remove all the spark plugs, leave the key off, and then try turning the engine over by hand. If one of the cylinders is filled with coolant, it will come out of the spark plug hole when the crankshaft is rotated by hand. Don't try rotating it with the starter, you can bend or break a connecting rod that way.
If coolant comes gushing out of a spark plug hole, then you know you have a bad head gasket. If you still can't turn the engine over by hand with the spark plugs out, then there may already be internal engine damage due to trying to start it with a hydro locked cylinder.
It should turn over by hand very easily with the plugs out. Take them all out at once, then try.

Did the engine overheat for long periods of time?