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.
On the subject of finance, you need to produce realistic financial details. How much money will the business require? What are the expenses required? How much tax will you need to pay? What are the profit margins? Do you stand a good chance of achieving these sums, and how? Finance plans should include income statements, cash-flow statements, balance sheets and profit analysis. This should form a big part of your business plan, in order to convince the vendor or bank manager of your credibility.