It's been said a couple of times, but I cannot stress enough how much you seriously need to sit down and physically WRITE OUT a business plan in full before doing anything else. This is a step that is too often skipped, but is essential regardless of the business size and will help you to define and focus your objective using information/analysis; allow you to use it as a selling tool for financing; uncover omissions/weaknesses in your planning process; and solicit opinions/advice from people, including those in your intended field of business (highly recommend you seek this advice from a good set of experts as it is necessary to prevent you from undergoing any unnecessary hardships).
A business plan generally consists of a sound business concept, your market/industry, location, management, financial control (how much it'll cost to start it/operate it and when you expect to turn a profit and how much), business focus, mindset to anticipate change (a HUGE concept to consider when building any business as roadway changes, construction, economy, heatlh, etc. (things out of your control) could drastically affect and thus bring down your business--sadly a lot of businesses suffer or go under do to these types of changes alone).
Fyi: avoid optimism. Be extremely conservative in predicting capital requirements, timelines, profits. Few business plans correctly anticipate how much money and time will be required. Hence you really need to sit down and do your research. And though you stated it'll be just the two of you, management and accounting are two areas where a lot of businesses either fail or drown in. You can have a great business, but if you don't have proper management (particularly of people), said business will suffer. Thus any type of business management and accounting class will help.
Some helpful links:
http://www.planware.org/businessplan.htm (kind of a "how to" for writing a business plan)
http://www.bplans.com/home_health_ca...summary_fc.cfm (a sample healthcare business plan you can skim through)