First Snake Vivarium questions

[GenShotgun]

Hi guys!

I'll be getting a male hatchling checkered garter snake soon, but need help with properly making an enclosure.

First off, i've got two tanks at home that i think would be suitable for a hatchling. An exo terra breeding box(large), and an exo terra medium flat faunarium. Which do you guys think would be more suitable? The breeding box is longer and wider, but not as tall as the faunarium.

I would prefer to use a sand based or wood bark chipping based substrate, would these be suitable?

And lastly the heating, this has been confusing me the most. Does the snake require to have a heat lamp at a certain spot to bathe in? Or is a heat mat alone sufficient provided the correct temperature and gradient is provided.

Would really appreciate any help, as id hate to harm the snake in any way.

Thanks!