You need an extremely detailed business plan. It needs include: your mission, your goals, how you how you're going execute it, and risks. Risks is every obstacle you could face. Competitors, financial risks, risk that your potential customers simply are not interested. You need a contingency plan for all those risks, if it possible. Then all 4 of your partners need discuss how you're going share percentage. Could be base on how % cash put in or other assets, or you just come to written agreement.(talk to a cpa about former I'm too buzz to explain and it been a year since I've done partnership accounting.)
A great plan can falter if you crap out on execution. Many people think accountants care about bottom line and salesmen care about top line. Me, I care about lines in-between. That where the art is, you can learn a lot about manager's style. Or use it as base to find parameter to explore to learn more. I definitely base the business on limited liability. Just my .02 or however it worth. Time for another beer