First of all, you're basically asking for a wide range of legal advice, which is off-topic here for any number of reasons. See https://law.stackexchange.com/help/dont-ask
If you're going to start such a business that is open to the public, lets members of the public interact with loaning their personal property and handles financial transactions, you really must have professional legal advice for all aspects of such a business, which includes but are not limited to: drafting a TOS, advising you on the federal and state and banking laws that cover financial transactions and credit cards, advising you on state and federal privacy standards for user information, advising you on what types of insurance you need for your business, and advising you on the technical aspects of the App itself. Without professional legal advice, you are opening yourself up to considerable liability.
My question is what protections can I offer myself as well as my
That's far too broad of a question for LSE. A lawyer can advise you on what legal protections you need for yourself and your business entity and what you can offer or disclaim in a TOS.
I imagine at bare minimum I could have in the TOS a disclaimer that
I'm not responsible for anything but then people wouldn't be inclined
to risk their stuff.
If you read the average TOS for a web-based service, you will see that many businesses disclaim almost all liability for their services, or at least what they legally can disclaim per state and federal laws But, those TOSs are drafted by law firms; that is nothing you want to attempt yourself.
Is it possible to store card info and if the user doesn't return the
item I could charge their card for some predetermined value they
agreed to before renting it? Sort of how Uber charges you extra if you
damage your Uber drivers car. How would I stop fraudulent charges
Yes, you can store credit card information for your customers, and do chargebacks, fraud checks, etc., but all of those banking activities are covered a very strict state and federal laws. You absolutely need both legal advice and competent programmer who knows how to develop apps that correctly handle financial transactions and securely interfaces with servers and banks.
Is it possible to get some sort of insurance? I'm a lone dev so I
don't have much upfront money or reason for a bank to trust to insure
Yes, you do need insurance; yet another question for a lawyer.