You can add 2 to 3 male guppies in a 5 gallon tank along with your shrimps. Adult male guppies can grow upto 1 inch in length, perfect for 5 gallon tanks. They are hardy and can survive in any tough condition.
They are also calm and vibrant in color which makes them fit for your planted aquarium.
I will keep 7 to 8 male guppies in a 10 gallon tank and I will make sure that I have the best tank filter for my guppies. Snails are an excellent choice for your 10 gallon tank.
If you are looking to lower the number of guppies and add more tank mates for your guppies then consider molly fish...