Metal backplate can help dissipate heat. It acts as a heatsink somewhat , especially If you have any air flow across its surface.
If I were you, I would start mining with something simple. For example, from TON coin mining. As far as I know, TON (former GRAM) mining is profitable at the moment and remains profitable as long as the mining will be available. But the possibility of mining may just disappear because right now it remains ~74M coins available to mining from giver-contracts.