German Blues should be kept in pairs (1m/1f). They do not like being on their own.
Otos need a mature tank. They are delicate fish and will probably end up dead if your tank isn't well established. If it is mature then you have no problem.
Another cory to make it up to a group of 4 wouldn't go a miss. They love each other's company.
The number of tetras you have chosen and the single dwarf gourami sounds fine.