A few questions for a Dart novice:
How early can we get breakfast on Sunday morning at the AGM venue?
Usualy not very early, but we could always gang up and ask The Management to give us an early breakfast.
There is a motorway service station near the AGM venue.
Can we get our start proof of passage at the AGM venue?
That should be very easy. If they have a rubber stamp, then you might be able to get it done the day before you go and just write down the time you leave.
Having had a quick play with potential routes and control points Lake Vyrnwy (Llanwddn) looks tempting.
There is a good cafe at Lake Vyrwyn (near the dam) I like Lake Vyrwyn...