1. Attacker might able to steal private key after user make a transaction from special address,but how do you plan to prevent this accident?
Only if you download a phishing wallet and leak your private key or you use custodial wallet and get trapped by phishing one, login with info which is stolen later.
3. Assuming a transaction is reversed, that means blocks would become invalid since it's hash (along with all next blocks) will become invalid? How do you plan to solve this problem?
Transactions are irreversible. In addition, the older a transaction is, the less chance to reverse it sucessfully. Because cost will become more expensive with older transactions.