I took a CFP course that allows me to sit for the CFP exam and one of my classmates was a CPA with 30+ years of experience. He was taking it because he was expanding his business into financial planning. He got into it pretty much the same way your friend is offering. He was getting referrals from a business associate that needed the expertise of a CPA beyond what a CFP could handle. He in turn would refer his clients that needed financial planning advice that went beyond tax planning, business structuring, and one that would serve as a fiduciary.
The majority of fee only CFPs mostly deal with high net worth individuals or small business owners. Those clients typically need a CPA in addition to a CFP to structure their businesses appropriately, select and manage retirement plans, and file their personal and business taxes.
One way you could structure a partnership with your friend would be to work as a financial planner. Charge the firm's standard fee based on how complex the client's financial planning needs are. Once you get beyond a certain point in tax planning you would inform the client that you will be putting on your CPA had and charge them an hourly rate. This would have to be all up front of course and itemized on your clients invoice. But it's what any CFP would do if they had to refer their client to a CPA anyway. Your friends firm could be a one stop shop.
It seems like your background is mostly on audit and corporate tax and you might have to brush up on the more personal side of tax like, investment, estate, insurance, and retirement plan setup. However, I can't imagine that would be to hard for someone that already has their CPA.
Sitting for the CFP is cake compared to sitting for the CPA according to some of my classmates and instructors. If you have a certain number of years dealing with clients as a financial planner you don't have to take a course and can sit for the exam, hence why your friend said you could take your exam in 2 years. You would probably have to get the books, review them like 15-20 hours a week for 6-8 weeks, take a one week test prep course, and then study full-time for about 6 weeks before the test to give you the best shot of passing the exam. It's a one day test, two three hour sessions.
If you are concerned that you would only be viewed as a financial planner, I wouldn't be to concerned with it. Having that CPA is currently worth more than a CFP designation, but together you can pretty much pick and choose who your clients are and how many hours you choose to work. Assuming you can turn down all the money people will throw at you.
Feel free to PM me if you have any specific questions.