A: The LLC is a good starting point for asset protection. How you operate the LLC, and in particular the LLC's finances, is even more important. You should be careful to keep the business's finances separate from your personal finances - for example, don't pay the rent or mortgage on your home out of your LLC bank account. And of course, liability insurance is your first line of defense.
A: Probably the primary difference is that a convertible note is debt, with interest and a maturity date. I do a lot of work with startups, and I rarely see convertible notes used anymore, and never see KISS agreements used. SAFEs are much more prevalent. That being said, there are a lot of different variables in all these instruments, and you should never just download a template and use it without customizing to your needs and discussing it with an experienced startup attorney. There are also securities law considerations. Raising financing from investors is not a good DIY project.