good morning.

I believe you are over stocked with the fish you have in that 14g tank. Are the gourami's in your tank dwarfs? If they are not, I would, if it were me, return them to the LFS.
question 1: IMO, Every time you do a water change you should vacuum about half the gravel, and do the other half at the next water change. Not all at once. Or at least a third of the tank at each water change. guess it also depends on your water change schedule? How often do you change water?
question 2: Your external filter is a hang on the back kind? If it is and you have water falling over the surface and showing movement and bubbles you should be ok. But, most folks do use the air tubes, air stones or wand w/pump. It helps to oxygenate the water and is beneficial for the fish. Especially if they have a larger tank.

~ kate