You can always try! Two pair of the Gouramis is better than one Betta fish. Just keep a close watch to see what happens. Of course, you must always provide enough plants, grass and anything like decors, rocks or driftwood for the shrimps.
I just want to say that the heater is overkill. I don't even have that strong in my 55. If it malfunctions, all your fish will be cooked. Stocking seems okay. I don't know some of those fish. Great thing about Malawi, ya can crowd them to lessen the aggression as long you have adequate...