as of now (acording to our lawyer) mmj has not bin clasified in any catagory, this is not to say it is not a taxable item, tho it is important to remember that anything soley created from your effort or "the sweat of ones brow" is somthing you already own and is not taxxable as income anywhere in the US as long as it remains in the state of origin.. $ .02 HHB
Like everywhere else, the attitude of the cops and their political bosses varies from county-to-county and town-to-town. Stay under the 1oz per patient limit, the 6 plant per patient limit, and always carry your card and you should be fine. You can only be a caregiver for patients that specifically designate you as one for them. So if two patients designate you as their caregiver, you can maintain 12 plants and have 2 oz on hand available for them.
Alot of Montana cities have placed temporary moratoriums on new caregiver operations until they figure out how to handle them. The industry is just now starting to take off.
As for tax liability....take the advice and see a CPA. I'd suggest that you form an LLC or S-Corporation, as that will limit your personal liabilities. And as with any business, document everything.