One thing to consider is voltage in. Most of the all-in-one (AIW) cameras require something like 3v-5v power. You should NOT use BEC power from your ESC. You might be OK if you keep the output to 25mw, but at 100 or higher I would not suggest it. I did this with a 200mw unit, and it burned up my ESC mid-flight, and I lost all control of the model and broke pretty much everything as a result of the uncontrolled decent.
I've gotten around this a few ways since then, the easiest is to simply power it with a 1s mini-quad battery, but that does add extra weight, and you need somewhere to put the battery. I've also powered one through the balance port on my battery, just using one of the cells. This causes the cells to not be balanced at the end of the flight, so you always need to balance them again before putting them to storage. Lastly, you can use a separate BEC for only the camera, but again - extra weight, more space needed, and complexity in wiring. There is one camera that I know of - the ZOHD VC400 which can take full voltage from up to a 6s battery. It's about $40 though, so double the other suggestion, but it does also output 400mw. There are probably other cameras that can take higher voltages - I haven't shopped around much though, so I don't have any other suggestions.
