Yup, you'll likely need commercial/ Limited Liability insurance.
If you allow people on your property with RV/trailer hookups, that'll add extra and you'll need more insurance for that.
Don't forget to figure out about storage(for feed/bedding if the owner has nowhere else to keep it) and weekly fees.
Have it stated that you use 'X brand' of bedding and if the owner wants or needs to use something else they must provide it and you'll discount the fee as you'll not have to use your own bedding.
If you have campers you can offer for a small extra fee to muck/ feed. This can be a liability for you though as you never know how a horse will react.
For short term boarders who need full care or even partial care, have a separate price list for them. You can charge by the week and/or by the month, providing a discount for the longer they board with you.
Billing: You'll want to collect upfront, debit or credit card or cash, no checks or money orders, always provide a receipt and keep a copy for yourself.
My mom learned the hard way about collecting payments. She owned and ran a roofing and home improvement company for years, although you're not supposed to pay upfront for these types of services (roofing/ home construction) collecting payment at the end could be a big challenge. Especially when people would give bad checks or fake money orders.
"They see me rollin, They hatin, Patrolling they tryin to catch me ridin dirty"