what should i be concerned with?
The biggest thing one should be concerned with is getting caught and getting arrested. That is numero uno on the priority list. Everything else is second fiddle.
I see you are from Missouri.
First off, let me tell you that Missouri has some hard core aerial eradication that goes on. Not only local units but the Highway patrol has 2 helicopters and several airplanes they use. The National Guard also goes out looking as well. They set up remote cameras in MO and during this past summer the Highway Patrol caught someone using a live turtle cam.
I wouldn't grow very many. I wouldn't put them packed in close together. I wouldn't do alot. Don't put them in a pattern. Don't use irrigation equipment such as sprinklers and hoses. Don't even leave a bucket. This stuff is what will make it easy to spot you from the sky.
If you only have 3 acres and there are other people's properties bordering that 3 acres than you may want to consider unless you have heavy hard core brush to hide them in. 3 acres isn't very much land at all.
If you are a complete novice then no answers to this thread's questions will be enough. You need to research what you have to do to be successful and plan every major step out ahead of time so you are ready. There is a ton of information available on this site as well as many others for you to know what to expect and what needs to be done start to finish.
If you are going to do it in a place like MO and its illegal then you want to be as prepared as possible to at least give yourself a chance to make the risk worthwhile. I would start off pretty darn small for your first time and at least learn what you are doing and get it down pat before you up the ante and try to grow any large amounts.