I can't comment on the Betta, but from my experience, having two of any Gourami can be hit or miss. A 60% planted tank is just asking for Cardinal Tetras ... especially if you add a black background and dark substrate just adds that extra pop in the Cardinal Tetras colors.
I'm not as familiar with the congo tetra, but you could also consider colombian tetras, figure 8 - 10 shouldn't make the tank look too full. Finally I've taken a liking to rummy nose tetras, they stay around 2 inches or less and their colors compliment the Cardinals ... IMO
75g Planted Barbs Denison, BlackRuby, Tiger, Albino Tiger, Green Tiger, Cherry, Gold, Checkered, Odessa.
NonBarbs Cardinal, Neon, RummyNose, Bloodfin Tetras, Z. Danios. 1RTS. Amano, Bamboo, Ghost & RCS. 20g Long Shrimp Tank RCS, Tiger, Amano.