So, the "one inch - one gallon" rule is a little deceptive, as the bioloads are different for fish, too.
I think the guppies would definitely be fine, I'm not sure about the gourami. Best rule of thumb is to check it with
AqAdvisor and see what it has to say. It'll double check to see if anyone would be overly grumpy or not.
Now, there's always this rule: Every fish is different. Just because something works for one, doesn't mean it'll work for someone else. I've put fish together that other people would never do, purely because of the size differences. (i.e. Angelfish and Neons). Worked for me, but usually doesn't apparently.
Now my angels and neons are separate, as my angels are getting older, but you see my point. I didn't know any better, but now I do.
My 10g has 5 cherry barbs and 1 male betta and 3 plants.
I didn't want to upset any balances too much, but then again I was being a little chicken cause they're my first plants.