Erythromicrons are not as active as some danios, they're more closely related to celestial pearl danios & their behaviour is similar, so they don't need long tanks for swimming room.
Try & get more females than males if you can
They are shy fish but if you plant the tank well & give them plenty of hiding spaces they'll feel more secure & you'll see them out & about more, they should be fine with guppies just keep an eye they get enough food as they rarely if ever come to the surface