Coinbase to Metamask – How to Import Your Wallet

This question is already answered here. Just for the shake of no link only answer.

DO the following steps to import your private key to geth and get a keystore file:

• Open Notepad
• Paste key into notepad without any extra characters or quotations
• Save the file as nothing_special_delete_me.txt at C:\
• Run the command, geth account import C:\nothing_special_delete_me.txt
• After successful import, delete the file at C:\nothing_special_delete_me.txt

If you don't want to use or you don't have geth. You can create keystore file using node and ethereumjs-wallet for same. (Ref: here)

var Wallet = require('ethereumjs-wallet');
var key = Buffer.from('efca4cdd31923b50f4214af5d2ae10e7ac45a5019e9431cc195482d707485378', 'hex');
var wallet = Wallet.fromPrivateKey(key);
wallet.toV3String('password');

The output of the last command is content of your keystore file. Just paste this in a json file and put this in .ethereum/keystore folder.

Ethereum seed phrases are based on BIP-39 standard. You can import the same seed phrase across multiple wallets. Some wallets might support only 12 or 24 word versions, but MyEtherWallet and MyCrypto support all formats.

You also have multiple questions in one question. It is not possible to mark questions answered. I suggest you open one question per question.