You have the general gist of it. If you send more drones, you will get more target information, while that may be bad for the drones if you lose them, it is by far, cheaper than losing your attack due to lack of intel on the target.
Each target planet may be attacked up to 6 times per 24 hour period, by each player. So if you and a buddy attack individually at a target, you could jointly attack 12 times. If you attack WITH each other ( a GA, or group attack) you are limited to 6 hits per planet.
Hope you are enjoying the game thus far (which uni are you in?). And feel free to post as many questions here as you wish. There are a number of "old-timers" more than willing to help; and remember, there are no stupid questions. The game is far more complex that what it seems on the surface.