Binance is not a wallet, it is an exchange.
If you use 2FA and other security, and you are able to secure your wallet, your friend would not be able to access your Binance account. But exchanges should be for trading, not holding.
Exchanges are often hacked, even Binance has been hacked before. Do not leave your coins on exchanges.
Use a wallet instead of an exchange. Use a wallet, have your keys, which means you have full control over your coins on blockchain.
Should I send all of my usdt and busd into my desktop electrum wallet for long term savings?
Not your Key . Not your Bitcoin/cryptocurrency so yeah it is perfectly act to send all your funds each month to your Desktop or any electrum wallet that you wanna use , this will add security for your funds though if you have 2fa in Binance then your funds will also safe but putting in electrum is much safer.