These are all good answers. There are really three things to keep in mind...
1/ You can grow enough for your own medical use and to ensure a continuous supply. This point is put first because it is the trickiest, but the most broad and speaks to the spirit of the law. Pay close attention to points 2 and 3, because if you exceed those, you will have to justify every gram and your medical use.
2/ Under section 4 and based on court rulings- 12 plants are considered presumed continuous supply. If you don't exceed this at any one time (any stage plant), you should be ok on THIS point (continuous supply)
3/ Under section 4 and based on court rulings- 2.5 ounces of usable cannabis is considered presumed medical use.
Now here is where the sticker is- if you have more than 2.5 ounces, AND/OR 12 plants, you are in Section 8 land and have to prove EVERYTHING down to your bonafide relationship with your doctor, every gram of cannabis, and every plant. You also get to hire an attorney, pay for an expert, and devote 18 months of your life and possible freedom to proving your point. You also get to do this if you leave your grow unsecured (read unlocked), transport it incorrectly, get involved with transfers outside your registry associated patients, or violate any other provision of the Act.
Oh yeah, you can be in perfect compliance and run into a LEO with an attitude who can, right or wrong, charge you and leave it to the courts/jury to decide if you were in violation. So the only defense is don't come to the attention of leo for your grow, domestic violence, jay walking, having a taillight out, or even posting too vigorously on Facebook or about news stories on public sites. Keep it quiet.
Dr. Bob