The area in which you are working is quite complex both in terms of describing inventions and in terms of the changing legal landscapes. An expert is definitely suggested. Even then, the terms of an agreement would be difficult to protect under patent law. This makes such a business model harder to protect than others. That said, there is often some technical aspect to software that is patentable separate from the business model itself, so you may want to look there as well.

I have very little advise on how to go about the process. I am an expert at Patent Law and can easily review people's work to determine its quality. That said, I could not do that for at least 10 years while working as a patent professional as the small nuances, etc. make it difficult to see what is poorly thought out vs. what is very well thought out - they often appear similar to an untrained eye. Most people look for the most thorough description, though this is not an indication of the planning and strategy in the application.

Most noteworthy, noone really reviews patent work, so even success of practitioners may not be the best indication. I know the answer is not helpful, but it is honest.

Here is my short checklist that anyone can look into:
1) Do they have their work reviewed and by whom?
2) Do they work with other attorneys to improve their work quality on a regular basis?
3) How do they approach strategy for claims?
4) What is their success rate for broad claims?
5) Do they handle a lot of software applications?
6) When do they call for help?

General questions include
1) Do they bill by the hour or on a fixed fee basis?
2) What is the time frame?
3) What do you need to do?

Every client has a best fit representative so don't think that there are best answers to the second set of questions. I have worked with excellent entrepreneurs who love working with me and with others where the relationship was better handled by someone else in my firm. Personality, style, etc. play a big role in the feeling that you are being well-protected.

In general, I personally look for someone who is business minded, who requires no work from me, who has their work reviewed very regularly by people from other firms, who call for help often, who handle a lot of software, and who bill on a relatively fixed fee basis for the drafting work.

I hope this helps.

I have written and filed three patents with two different startups and am currently advising a third startup on patent process. There are different stages within a startups growth in which it should worry about an do different stages of the patent process. If you would like to discuss it further let me know.