If you business is new and success is uncertain do not incur any expenses to incorporate. Once you are certain that the business has staying power your choices will be to incorporate only if you need legal protection. If so most clients will be fine with a simple Subchapter S corporation. Certain clients such as real estate investors, some New York City corporations and those with complicated profit sharing arrangements might be better served creating an L.L.C, (a Limited Liability company).
A million (or at least a thousand) dollar question. Most of our clients that are using a computer based bookkeeping system use quickbooks as that is our area of expertise and it is truly an easy system to learn. It looks and operates like your checkbook and is very intuitive in its operation. Having said that we do not always insist that our clients use a computer based system. For some, with minimal transactions every month it will not save them money in accounting fees. If it does not make your job easier for billing or paying your bills then it may make more sense to use a manual system.