Well, the law is quite specific on one of your points, Cgrizzle, but fuzzy on another. Here's a quote from the actual legislation that passed, this regards weight and plant count:
"(b) A primary caregiver who has been issued and possesses a registry identification card shall not be subject to arrest, prosecution, or penalty in any manner, or denied any right or privilege, including but not limited to civil penalty or disciplinary action by a business or occupational or professional licensing board or bureau, for assisting a qualifying patient to whom he or she is connected through the department's registration process with the medical use of marihuana in accordance with this act, provided that the primary caregiver possesses an amount of marihuana that does not exceed:
(1) 2.5 ounces of usable marihuana for each qualifying patient to whom he or she is connected through the department's registration process; and
(2) for each registered qualifying patient who has specified that the primary caregiver will be allowed under state law to cultivate marihuana for the qualifying patient, 12 marihuana plants kept in an enclosed, locked facility; and
(3) any incidental amount of seeds, stalks, and unusable roots."
Here's the clear part: If you are a CAREGIVER, you're allowed to have 12 plants and 2.5oz PER PATIENT. The law is very specific on that. Proof can be found on the State of Michigan website, just search for medical marijuana and you'll be taken to the section where you can find all the info they currently have, including PDF application forms.
Now for the fuzzy part: Dispensaries and Compassion clubs. These are not mentioned in the law, so there are two prevailing theories out there. 1.) It's not mentioned, so it's not legal. and 2.) It's not mentioned in the law, so it's NOT ILLEGAL.
Now, take note of what I typed for point #2 here, cause this is what lets the lawyers have fun in court: The argument on theory #2 is that since it isn't made ILLEGAL by specific wording, that is is in fact... LEGAL. THIS IS NOT TRUE. Statutory law fills in these gray areas and we haven't seen any cases tried yet in Michigan. For those who don't know what a Legal Statute is, it is a precedent established by a judicial ruling that gives an interpretation of the INTENT of the law (prolly butchered the hell out of that, but the point is clear). Statutes eliminate the needs for our legislators to keep going behind themselves and re-structuring laws that are poorly defined.
Due to the interpretative nature of Statutory Law as opposed to true Legislation, I think it's reasonable to assume that in the state of Michigan, Compassion Clubs and Dispensaries will be illegal for the foreseeable future. The law is just too new to the state for judges to be liberal enough in the interpretation to take a chance on their career with a decision like that. Michiganders don't have the experience of Californians when it comes to dealing with the apparently "lax" (The words an anti-cannabis activist might use. Remember, most of the true anti's think that even Marinol should be illegal) restrictions. At a bare minimum, people who abstain from cannabis use are going to be very cautious, and nervous of increases in crime. We have almost a century of social propaganda to overcome and we haven't gotten out of the baby steps yet.
Hope this helps, and ANY information you need, forms too, can be found on Michigan's state website. Just search for Medical Marijuana. Unlike some state websites, this one is organized pretty well.
Edit: As a side note, I honestly don't understand why anyone would want to team up unless you have too small a house to accommodate a 5 patient growing operation. At 12 plants per patient and a full patient roster, that's 60 plants. There's no reason you shouldn't crank out enough bud to service them all if you plan your grow out well and get your plant rotation on track.