Check the battery earth to the engine block, if it comes loose it causes a high resistance in the starter motor circuit (not enough umph to kick it over).
You should be able to check this by putting a single jump lead from the
"-" (negative) on the battery to the engine block or the starter motor housing.
You said your battery is good, how many CCA's is it? Should be minimum 800cca.
Coolant smell
Don't know
Just continue to monitor the coolant bottle for oil contamination or fluid loss.