Things about Feast Planning I've Learned the Hard Way

1. Do a test feast. You may not be able to do every dish as it will be done at the event (you can't spit roast a whole pig, for example), but you'll learn what works and what needs tweaking, and you'll have recipes you can confidently hand to your kitchen staff. Be sure to take notes when you're cooking the test feast, so you can make sure the final recipes accurately capture your process.
2. Use the skills your volunteers have. If you know someone is a veteran feast cook, you can set them at a dish and stop thinking about it. If someone is brand new but eager to help, you should give them very specific instructions on what to do - there are useful jobs for everyone.
3. Reduce the vagary of tasks. While you will have people of varying skill levels, you're more likely to get a large amount of unskilled labor than skilled labor. The more exact your recipes are, the less expertise a volunteer needs in redacting recipes.  
4. Put up large sheets of paper listing the order of the dishes, and what goes in each. This will let anyone in the kitchen easily see what dishes need to be served when, what dish their current project is destined for, and what potential allergens are in each dish. You could even use one such list as a checklist of what's been cooked/plated/served, making it easier to identify what needs attention right now.  
5. Map out how to cook your dishes with the tools you will have. If one thing needs to take over all your available ovens for three hours, you need to have worked out in advance when it can have those resources. To do this, you need a thorough understanding of what equipment you have at the site, and whether it has any quirks (ovens that don't work, sinks that aren't hooked up, etc.).
6. Plan to be flexible about your starting time. Forces beyond your control may well push the feast later, or in rare cases you may be asked to move the start earlier. This can wreak havoc with any feast, so the least you can do is think through some contingency plans in advance.  
7. Work out how long each dish can stand. If you're making hot fritters, they either need to go out right after they're made or you need warming ovens to keep them in. If you try to serve them in the first course this can make your timing very tricky, especially since you probably won't be able to control exactly when you start.  
8. Do things that can reasonably be done in advance, in advance. If you need 20 pounds of chicken shredded, or 18 heads of garlic peeled, think about doing them ahead of time. Your volunteers will be happy you did, and it will remove work that otherwise could become a bottleneck on the day itself. You generally don't need to chop vegetables in advance, or pre-cook meat, or anything else that's best when it's fresh - just anything that's tedious, and can sit for a day or two. 
9. Be realistic about what people will eat. (Or, Nobody Eats the Barley.) This is notoriously hard to get right, but there are some tendencies you can work with. People will eat lots of bread and meat, a fair amount of stew and pie, not that much fish or vegetables. If something will seem weird to the average palate of your diners, make a lot less of it. If people love it at the test feast, AND the test diners are a good representation of the real diners, make plenty of it.  
10. Remember that people get full. Everyone is hungry when the feast starts, so they eat a lot of the first course, and less of each subsequent course. You can use this in various ways: you can put cheaper foods earlier (to a degree. Don't put the best food out when no one can eat any more); you can entice people to eat weird foods by serving them first, though if it doesn't work you'd better be quick with the second course; you can keep all the courses small so people stay hungry longer, as long as you are very sure of your portioning and the timing of your courses. It can be risky to rely too much on any of these approaches, but it's something you need to be aware of. People simply will not eat as much meat at the end as at the beginning, all else being equal.