You would first do a P&L for the present year for your existing business and the first year and as many years after as you would like to have your plan cover. Your existing business financials will be the foundation for building yourself a business plan for as many years out as you want. This data will tell you a number of things but first if you want to build your plan around what you want in life, you would need to decide some things about your life: 1. You would need to decide how much income you would like to have for yourself for each of the years you plan for. 2. You would need to determine what kind of profit margin you would want from your business for each of the years. 3. And by combining these 2 things into a P&L format you can develop a financial business plan that can extend as for into the future as you would like. 4. The first thing it will show you is how much sales you would need each year to give you the income and profit you would like. Once you see the sales needed, if you know your business well enough, you should be able to estimate those additional expenses needed to overcome capacity constraints that will occur as your business grows.
But do not be too paranoid, make sure you are showing it to people you trust, whose feedback you welcome and can be genuinely useful in guiding how the plan takes shape. Very often when working as individuals we get very close to certain details and miss out a big thing that has slipped your mind. You can concentrate so much on essential financials and supply logistics, but overlook other issues like marketing or opening times. By showing the plan to someone you trust, they can have a look and see what might be missing or worth developing more. Getting that valuable second opinion on how robust your idea is will put you in a much better position to start and keep going successfully.