popping out of 5th, thats most often a sing of internal wear on the gearbox so i'd expect a new box to be needed in the future, the problem tends to get worse and worse. sometimes if you're lucky the gearbox linkage just needs adjustment, but on the marea the linkage isn't adjustable so i doubt you're that lucky unless the rubber bushes of the linkage are excessively worn.
as for the fan coming on, is the temp gauge working ok? i/e/ does the gauge say its slightly above half way when the fan comes on? if thats the case you could have a bad temp sensor. if the gauge is working fine but the fan still comes on before it should i'd try changing the relay.