Yes, get the OMC factory manual, don't get aftermarket. The others leave out critical data.
If you don't want a nightmare of hard to reach bolts since 110/115 hp has bubble back exhaust, get the proper powerhead lift tool and an engine hoist to pull powerhead to service it.
The alternatives are spend a long time trying to remove and re-attach bolts, or cut access hole for the thermostat bokts (Not recommended)
On a 90 to 100 hp, the flat exhaust makes changing not as nightmarish.
Regarding the OMC gasket sealer required, just get permatex aviation form a gasket.
Make certain the small hole on the thermostat is clean and no obstruction before assembly.
Just use enough sealer to get it done, too much may get into that small hole and impede the ability for the outboard to run cool at idle.