You say you've run the numbers; I'm sure you did it yourselves. $200 a day split four ways is gas money. Where is the $600 per month to pay off the loan coming from? Have you added in equipment insurance? What if the camera is damaged or stolen? Now you have zero income and still have to pay for the camera. What about liability insurance? If the camera falls on someone they could sue you for everything you own. So you'd better set up an LLC to protect yourselves and your assets. Has a legal professional vetted your boilerplate contract for loopholes?
You're hearing a lot of contrary advice, and probably a lot of things you don't want to hear. I run an audio post business. There are a ton of things I'm sure that you have not considered. I spend about six hours a week - not including marketing - doing all of the "unfun" stuff involved in running my business - the books, billing, taxes, equipment and software maintenance/upgrades, "housekeeping" (vacuuming, dusting, garbage, cleaning the bathroom), maintaining the web-site, research, etc. And there are all of the incidental expenses; HVAC, equipment and software maintenance/upgrades, insurance, communications (phone, 'net, web-site, ink cartridges, FedEx, etc.), housekeeping supplies (paper towels, Windex, toilet paper, vacuum bags, etc.), pads of paper, pens/pencils, CDs, DVDs, disk drives... Then every few years there's big expenses like a new computer and the associated software upgrades. The list goes on and on.
It's "easy" for me because I have no one arguing with my decisions, at least about my business.
You have four people sharing the responsibilities. Do you all have a contract delegating those responsibilities? What if someone drops out? Does the equipment they purchased go with them? Who maintains the bank account? Who owns the business name? Even "stupid" stuff like - who is responsible for the gear every night after the shoots? Who does the maintenance? Who pays for the maintenance? Who takes care of the bills? Does that person deserve a few extra percentage points since they are running the business end of the business? If one person is bringing in most of the clients do they deserve finders fee percentage points? These kinds of things are very collegial in the beginning, but as the business grows the distribution and depth of responsibilities kills lots of businesses, the friendships fall apart and there is no paper work to back up dissolution positions; it can be worse than a divorce.