For Moralis to work properly, you have to host your pages through a server. When you open the HTML file directly, you will face this issue.
This has been mentioned in the moralis docs for your reference over here - Uncaught Reference error- Non Ethereum Browser
Hope this helps.
Your private key is stored in your browser.
Metamask ask you for a password to encrypt the private key.
No it's stored locally.
Always back up your private key. It's better to store your "mnemonic phrase" as they are human readable. A naked private key is hard to copy, and any error (a character change) can be lethal for your back up because you ...
You can do this by decoding the input data with sites like this. But you would need to find the ABI of the contract you are calling. IF the contract is an ERC20 token or any other standard token, a standard abi is sufficient.
You can find most ABIs via Etherscan when searching for the address of the contract you are calling.