Is it possible to import Substrate (Polkadot) address to Metamask?
No. Polkadot (Substrate framework) uses 256 bit address while Metamask uses 160 bit address
Can I interact with EVM contracts by using existing Substrate account (non-ecdsa)?
Any Substrate account could call EVM in Substrate, the address will be mapped into EVM compatible representation
I was able to deploy contracts in other networks, but contracts deployed in this network show "out of gas" error with the error code of 0. How do I fix it?
Contract size limits may differ in the network, it is recommended to lower optimizer runs of the same smart contract for adjusting the compatible size for the network. Please try testnet to tune it.