I think with any friend terms should be clearly layed out, even oraly.
Now if it were me and I am swampted and haven't charged the full amount, I would allow some delay if things are coming along. But I would eventually get down to it. I guess the delay can't be too long either.
Don't hesitate to ask him to put his word down for a delivery date. Letting him know that it is frustrating for you to be in the blue (that's to let him know), if he takes your business for granted, remind him that customer experience is indid important as well as reputation, and that for the moment the experience is a frustrating one.
Your rate is fine to start with small weddings or short half day ones.
Now since weddings happen longer after you have booked them, you need to have a contract that retains them while allowing for a reasonable amount of time to rethink or policies that allow you or them to bail in extraordinary circumstances.
The prob with the rate I see is that if you make your downpayment a percent based (say 30%) even if your contract threatens that you will pocket it if they bail for no justifiable reason, it's an expense that most people can bare if they decide to change photog last minute.