Well some people don't use an air pump and just like to have an external filter to create water agitation on the surface. It depends on how many fish you are keeping and their requirements. If you have good surface agitation it should be enough.
For adding live plants, it will only help very little and you will need to know how to care for the live plants. I suggest you take a look in the plants forum section if you are thinking about it.
A betta with a gourami, it really depends on the type of gourami. Some people are able to keep them together. If the gourami has very flashy long fins, then that might be a problem. IMO I wouldn't risk it.
