Dwarf hamsters don't "need" a same sex companion. They can do well in pairs or trios or they can also do fine alone. Syrians must always live alone.
For either species of hamster, Dwarf or Syrian, I would recommend using a large clear tub rather than a C&C cage. They can squeeze out of the regular grids (1.5" x 1.5" openings) but you may be able to build one of out mesh cubes successfully.
I have dwarves and syrians, both live in large sterilite bins and you don't need a lid if the walls are high. They can't climb out of them unless you have large houses that are tall and near the side of the cage. If you have cats, dogs, or other predatory pets that would pose a threat to them, then I would very much suggest a lid. The bins are always very easy to clean and I've never had a problem with ventilation.
To sex hamsters, they are fairly similar to guinea pigs, if you know how to do that. The males have a penis and testicles, with a large gap between the anus and urethra. The females have a smaller gap, with the vagina and anus rather close together. And they obviously have no testes.
I feed my hamsters the Mazuri diet for hamsters/gerbils along with a small amount of fresh veggies and fruit each night. Hope this helps.
