I'm going to try to make this short, but I'm sure it won't be. sorry in advanced. This is how ours runs and the people we have....and although we are known for great trials, we're also known for being kinda slow.
Positions (for at least one ring):
trial secretary (coordinates everything)
volunteer coordinator (makes sure all positions are filled)
ring steward (makes sure there's enough volunteers at the ring)
1-2 people enter in times (2 is more important when doing games that require adding up points)
1 scribe sheet runner (sometimes it's the person who enters the times too)
1 scribe (needed at the ring)
1 timer (needed at the ring)
1 gate (needed at the ring)
1 leash runner (needed at the ring)
2-3 jump setters/chute fixer (depending on the course, standard usually needs 1-2, jumpers needs 2-3)
And of course, course builders. Usually we have one main person in charge, and anywhere from 2-5 people assist with moving equipment. Our equipment is on the field the night prior (but not laid out as we don't have the actual course maps until the morning).
Sign up sheets for volunteer positions is usually either on the board at the gate, or near the course maps. One venue I run, uses a large white board, where people just fill in their names. That way, you also know where you need help.
I missed hospitality. Usually 1 person is in charge, but person usually recruits another person to help out.
Usually we have a briefing in the AM before the first dog on the line. In AKC, there's usually a general walk-through before the briefing (meaning anyone can walk). After the briefing, typically we get an 8 min walk through, then 5 minutes before first dog on the line. Typically, you check-in (put a check mark next to your name on the running order at the gate) sometime when you're walking (before, after, etc). And usually the gate starts calling out people who haven't checked their name off to make sure they are there. During the runs, the gate calls out who's at the line, who's on deck (next up), who's in the hole (after the deck person) (I think all that comes from baseball, lol). And then sometimes continue with a few more names to make sure they know they're coming up.
The person entering the scores is typically doing them as the dogs are running...because the scribe sheet runner should be getting them.
The scores are typically printed out (by classes), and put in a binder and also posted. You pick up your own ribbons. The only time we do photos is when someone gets a major title (MACH, CATCH, ATCH, etc). If you want to keep the presentations, maybe you can do it at the end of every class (not jump height). For example, photos only after all Novice runs.
Lastly, how to entice people to work? Vouchers. Usually, it goes something like this. If you work 1-2 full classes (e.g. 16" excellent standard), you get a lunch ticket. If you work more, you get a voucher for $$ off our next trial. Some will give out $2 per class. Some give more money. This works well when your prices are slightly higher than normal.
I think I covered it all. I'm sure I missed something.
Oh yeah, also look into purchasing a portable generator. That's what I've seen used when there are no power sources. Some are gas powered, others are basically big batteries. Usually we have one at each ring to run the timers and another one for the computers at the scoring table.
Of course, the same people are always helping out. that's the way it is everywhere. for our club, it's "mandatory" that you help either set-up or break-down.
hope this helps you a bit.
If we had 660 I think we'd take 4 days! 
Will need to make them more prominent and important to the triallers.