Thanks, Mike. I understand why the dirt guy recommends 8 inch pipe, as it is $20 a foot cheaper and has done okay for his other ponds. I figure it will likely cost $3k more(!) for 12 inch pipe in my setup, but in the long run, it will substantially reduce erosion on the spillway, as it carries more than twice as much water as the 8 inch.
And I will get a soil service to check compaction, as well. If you get a break, maybe I could hire you one day to take a look for any obvious problems. (Obvious to you, that is, not to me!) That won't be for a while, though, as it will take a week of dry weather to get things started again.