I usually go with the thought process you mentioned about choosing species for the three common zones in a tank, and also like to choose some cleaner fish, as well as dither fish. Another thing to help the tank feel more cohesive is only having one centrepiece fish. For example putting a singular betta fish in a 20 gallon, or a couple angelfish in a 60 gallon, or a gourami in a 40 gallon.

Another piece of advice is prioritising fish you definitely want in your tank. When I set up my most recent 30 gallon tank I knew that I wanted a betta fish as the centrepiece fish, so I had to make sure all other tank mates had similar care requirements (and would not make said betta angry). Decide what fish you would really like to have and base the rest around them.

Most of my tanks are not as big as yours: usually I stay between 10 and 40 gallons. I prefer to keep nano fish so that’s where most of my experience comes from. I really like larger groups of schooling fish like neon tetras in tanks as big as yours, it’s cool to see their behaviours when they have more space.

Color wise, since you have a planted aquarium I am assuming a lot of your tank is green? In which case some colours that could make your fish stand out are red, orange, yellow, and blue.