I'm sorry but that is completely inappropriate. You need to research your fish and their needs before continuing to buy more fish, that tank was already completely overstocked and several member advised you of this.
You can't simply say it is happy when you don't even know the needs of your fish. Maybe it is happy for now, but what you have set up is not going to work long term and your fish are going to suffer for it.
People that put goldfish in 5 gallon tanks also think there fish is happy until 2-3 years down the road it dies. What in reality they did was shorten their fishes life span by at least 10 years, stunt it's growth and kill it with organ failure because of it. Never giving it a chance to reach it's full potential and live the long healthy life it should.
Please research your fish and what they need and provide it for them or rehome them. The people on this site really care about our fish, we believe they are just as important as any other animal and deserve the best care we can give them. We tell you these things from experience and knowledge and because we honestly care about what is best for the fish. We aren't telling you this to be cruel or mean but you need to realize the care these fish need. A molly, neons and a pleco do not belong in a 6 gallon tank, let alone all at the same time.
I'm sorry I really am not trying to come off as bossy and in the end you will do what you want and I can't change that but reading this is upsetting because I do care so much for my fish. They are no different than my cat, dog or bird and deserve the same dedication and care IMO. Please do some research and really learn about your fish, their habits and needs and then ask yourself if this is where you want to keep them.