I would suggest that you add the shrimp and snails first as @Will Billy said. After a few weeks I would add the guppies and then just treat the entire aquarium with the med trio as @Fish Folk suggested.
I would suggest adding a pre-filter sponge and or a sponge filter as this helps give the bacteria that turn the nitrites into nitrates a place to multiply. You might also want to add some more live plants to help you with the nitrates when the bacteria starts doing its job. I hope this helps!