1. Yes it is. Don't use a password manager if you don't trust it's security.

2. Two points here. First is your encrypted vault is stored in Azure, which is a Microsoft product. Microsoft is the one who would have to be compromised. Second is if they were compromised and your vault was leaked (like has happened in the past with other password managers), the vault is encrypted. The encryption makes the vault useless to anyone would would try to read it (unless your Bitwarden password was really weak).

3. That someone gets a hold of your unlocked vault and has literally all of your online passwords, your email, bank logins, and the like.

4. The biggest factor in security isn't the program it's the user. Writing the password on a sticky note next to the computer, sharing passwords, getting phished, having you computer compromised, etc. The biggest thing you can do is to take steps in being proactively secure. Lock the vault aggressively, keep your computer and network secured, have a strong password, etc.

5. I assume you mean that you use 2FA to log into Bitwarden? Yes, that helps greatly. Say your Bitwarden log in and pass were compromised, the 2FA would protect you.

Re: the other posts saying to split into between 2 managers or keep the pass in your head
It increases the level of security sure. It's really up to you on how much convenience you want to trade for security. I trust myself enough to just have Bitwarden + a ridiculous password.