Since you have multiple homes already, an LLC may make more sense than an umbrella policy (unless you mean those are all personal residence/vacation homes and not rentals, in which case you wouldn't want them in an entity).
There are several considerations that can go into the analysis of whether you need an LLC or whether a large insurance policy will suffice. Will depend on several factors like the type of property, type of tenants, your risk tolerance, other assets you own, your estate planning, laws where the property is located, etc.
Any lawsuits would be limited to the assets of the LLC and not your personal assets (assuming you run the LLC appropriately and the corporate veil is not pierced). But, an LLC will not limit you from liability in total. You can still lose your investment in the LLC. If you're going the umbrella insurance route, make sure it will cover you for several things including just the routine slip and fall (like mold or earthquake). You'll also want to ensure you have a good property manager to look after the upkeep of the property if you are not there to notice anything deteriorating or which may need attention.
Creating an LLC in California would cost you a minimum tax of $800 every year. You would have ongoing filing requirements with the State and would need to keep business records and documentation. If you create an LLC, you will need a business account. Otherwise, if you hold them in your personal name with an umbrella you do not need a business account. If you are buying out of state, you can create an out of state LLC and register it as foreign in CA or you can create a CA LLC and register it as foreign in the state where the property is located. Either way, if you are managing from California, you are "doing business" in California and will be subject to the $800.
You also want to look at whether a pass-through entity helps your bottom line and your taxes. There is a new 20% pass through deduction you may qualify for that could help you, but not everyone qualifies. You should still be able to get this even if the properties are not in an LLC, if you qualify.
These are all things you will want to discuss with your attorney and CPA. If you need references for either of them in San Diego, let me know.
*This post does not create an attorney-client or CPA-Client relationship.The information contained in this post is not to be relied upon.Readers should seek professional advice.