I personally would wait until I get the 75 up and running before I buy more fish. your gourami's will likely come close to adult size before you set up this 75 and your filter probably won't be able to handle the bioload. Also another thing to consider is the possibility of a catastrophe. The tank very well may leak when you set it up or someone may bump into it with a sledgehammer. Also take a look at the convertor link in the chit chat pinned topics the third link down will help you calculate the oxygen requirements for your tank.
still overstocked but weekly 10% or biweekly 25% water changes you should be fine, depending on how many neons. Don't know if gourami's would eat neons I'd wait for someone who has experience with them together to comment before I did anything. gold gourami's are one of the most aggressive types so there may be a problem. hmm sylvia would be a good person to ask.