You don't have to assemble the pass before you load it. In fact if you buy it from a window at the RER at the airport they will just hand you the kit all charged up. The monthly charge is for a calendar month so if your weeks cross two months, you will need to go with 3 weekly charges or more -- To use it from the airport into Paris, you will need a 5 zone charge. If you charge for zones 1-2, you can buy a one time use ticket into town called a Parcours that is charged to the ND within 3 hours of travel. Since you are getting a monthly pass, you will be able to travel anywhere in all 5 zones on weekends with the 1-2 charge so if you can organize your trips out of town e.g. Versailles, Fontainebleau or whatever for weekends, you won't need the more expensive charge.
Otherwise with a 1-2 ND you can buy Parcours tickets for other zones that offer slight savings e.g. from CDG it is 7 Euros something whereas the usual ticket into town is 9.75.
The photos are postage stamp size 25/30 mm -- and any head shot will do -- color or black and white and on any kind of paper. We just cropped them out of snapshots and printed them on regular computer paper. Sometimes the clerk will assemble them, but at busy stations like the airport, they just take your money, charge up the card and hand you the kit to put it together, which you of course do before use. You can ask for the Parcours into Paris at that time if you are not getting the 1-5 charge.