Buy-Sell Agreements

In the next 2-3 years I will have an opportunity to buy into a contracting company with annual revenue of $18M. I know how to make money in this business, but I'm not familiar with this type of transfer. Currently the company has 1 sole owner and has been in business for 25 years. What type of agreement should I expect that the current owner will want? I'm assuming that because of tax reasons, he's not looking for a lump sum buyout? Also, how can I raise the money that will be required up front for due diligence (and I assume I'll need a broker as well to facilitate an agreement)?

Any advice is appreciated.