You have the right idea. I would NOT use a cover letter per-say. Those I feel should be used when you are applying for a job and sending in a resume.

I would do a flyer presentation with all the information on sheet in bullet style, and type up a business job resume with all your achievements etc. included. Most resumes have a "goal section" that you can elaborate what you could do for a potential client. Keeping it simple and easy to read is the key.

You mentioned going to a business gathering soon, I would hand out detailed resumes to those who showed a strong interest. Hand out the "flyer presention" to everyone attending that you meet, along with a business card.