You'll never see 6 ghost shrimp in a 55 gallon, so unless you want to play "find the ghost shrimp" I really think you should get more. Just don't get them from petsmart; a fish store will sell them for as low as 10 for $1 rather than $0.35 each. 1 per gallon is a common guide. As for the Corys, 6 would be the minimum for a 29 gallon tank. Of course you can always get some, and then decide if you want more. That's the fun of having a fish tank
But in my opinion and experience, a big tank with small fish looks best and is most enjoyable to watch when you have big schools. Other people may feel differently, I don't know. Don't care either. That's what's great about hobbies
For color I think orange flame tetras are nice. They stay in the lower half of the tank. I like dwarf neon rainbows for that tank size - they are fascinating to watch, very active and flash brilliant blues when the lights hit them right, and they will stay in the upper half of the tank.
There really are a lot of choices, some of which may not be available to you because of your location.
I like to build my tank around a centerpiece fish - often the largest fish in the tank - the one that makes people say wow. Not just because of its relative size, but because of its beauty and presence in the tank as well.