Hi! I've helped plan something like this before. I was not the one responsible to be the contact for the publishing company, but was asked to collaborate on the planning.
If I may suggest, in attempts to helping you to answer your quantity question:
1. Look closely at the type of group(s)/number of group(s) members available to contribute to your recipe book. You can pretty much be assured that each contributor will buy at least one copy each. That's a start. If it involves children's work, add half of that initial number for grandparents. (easy example, 10 initial books from contributors and 5 for grandparents would be 15.)
2. Depending upon when your publication date is and also your projected date to receive the final product - if it's due to arrive around Thanksgiving, for example, you should probably expect to double that initial order immediately (taking the number example above, this would put you at 30 books)! That is a time of extra cooking/table prep ideas needed, etc. Everyone looks for new recipes to serve their family and guests around holidays! (this is a hint towards timing/marketing your product as well!)
3. If it is a church group, consider the number of FAMILIES that are members/regular attendees. EVERY family may not purchase one, but others will purchase multiple to give as gifts, so you should consider 1 book per family (KEEP IN MIND "Step 1 above" when you add in this "family" count. Don't count them twice, or you could have several more books than you intend!)
4. If you are going to have a "tasting" of some of the included recipes, depending on the number of people you invite and the location of this event, you will want to add appropriately for that. (ALSO, keep in mind Step 1 and the 'family' count here.) For example, if you are having a "public" sale, (with or without the "tasting") you may want to add 30 books or so, depending on where you hold this sale, your community, etc. (Again, using the number example, you would be at 60 books + your "family" count.)
5. Many of these recipe book publishers offer price breaks at certain quantity orders and/or meeting their publishing timelines/requirements etc. As you begin to calculate these number suggestions, it would be wise to compare those numbers to any such discounts offered by YOUR publisher! (If they have not mentioned such discounts, it might be good to ask them about it!)
Oh, and if your group(s) of contributors are a church, you may want to have a copy or two of the book in your church library.
These are only suggestions. If my church examples don't quite fit your situation, I hope that it at least helps to get you started in figuring out your quantity question and also gives you a few marketing ideas. Your publisher may also have some extra guidelines on how to gauge the number to order. Don't forget to calculate the cost you will incur per book and your needed return for each - this should be considered in your quantity as well.
As for the one I was asked to help coordinate - we counted on 2 for each contributor. Added in 1 for each family that was not a contributing family. Added in 100 for the bazaar open to the public and an extra 50 for gifts/misc. It was a success; the actual purchases did not exactly match how the count breakout was done, but the end result came out all sold.
Enjoy your special recipe book! How fun!