Hello and congrats on deciding to get mossy frogs! They are awesome pets. I don't have T. corticale myself but both gordoni and asperums.
Crickets would be a better stable food. Avoid using mealworms for this. If you can, try to get your hands on a dubia-roach colony. They are crazy easy to maintain and mossies love them. They are a great stable diet for any frog.
My guys sings all year long. But it's much, much more when they're breeding. Mossies are really hard to sex. I think the females can sing too.
To my knowledge the base of the tumbs should turn pink on the males during mating. Could be hard to see...
Not sure here but I think it's much longer then 5 years with proper care and tank.
Hope this helps!