Well, in order to save some money on reception cards, my fiance and I got tri-fold wedding invitations with our names on the front, the standard wedding information in the middle fold, then the reception information on the 3rd fold. I would definitely do that...it saved us a lot of money because we didn't have to buy those reception cards. You could also add "Reception to follow at..." at the end of your invitations. I've seen people do that and it looked fine.
In regards to what you will need: A mailing envelope with your return address printed on it, an inner envelope, invitation, response card, a self-addressed stamped envelope for guests to return response cards and reception cards...you might want to include directions to the church and reception, as well as hotel information for guests that are coming from out of town.
In regards as to when to order them it all depends on who is doing your invitations. Once you have decided on the invitations you want, then you need to select a vendor and find out what their average time of delivery is. I would probably order them about one month before they are supposed to go out. This way it will give you time to address them, etc...
Good luck!