1. I read that never store all your coins in one wallet. So wts the solution? should I install two electrum standalone wallets and store my coins in both of them?
It actually depends on the users' preference on how they are going to safely secure their holdings. If you prefer long term holding, then I suggest you to diversify your crypto holdings to a coldwallet and a hotwallet. Use a coldwallet to safely secure most of your funds in the long run and use a hotwallet for your "daily spending" or transaction.
2. I have written seed on a paper to recover my BTC in case my computer got corrupt. What thing apart from seed should I backup to recover my wallet in case my system is corrupted.
The only thing that I think you should backup is the seed phrase nothing else. The correct question would be, "
How should I secure the nmemonic phrase/ seed phrase?"
3. Strong password is good enough to secure a wallet or I have to do something else also.
What particular wallet you are using?
Having a strong password will never be enough if your are not holding your private keys. If you happen to store your coins in custodial wallet with a random generated password from a password manager or 2FA turned on in it, there is not much guarantee that your wallet is secure as long as you are not holding your private keys.