Even better, use a password manager.
> 2. If possible, use a separate computer (an old one or a cheap one purchased for this purpose) for things like banking; if your family computer is the same one that you use for bank transactions you risk having your kids click on a bad link that results in a hacking.
Not necessary, use an up to date computer with Windows defender turned on and create a non-admin account for your kids.
> 4. Have antivirus software on your computer
Only use Windows defender, which is what the security community recommends.
Also use 2FA on all services which offer it.
Regarding the domain registrars, I would recommend Namecheap. They have a great support team and also offer 2FA, but I think it's only SMS based 2FA.