I'm no expert but I would be concerned about the insufficient watershed. IMHO this will guarantee a huge fluctuation in water levels throughout the year. This happens on my pond but we overcome this to some degree by have a deeper pond (mine is 17-18 feet deep). Which brings me to my next concern - without sufficient watershed you should have a deeper pond (IMHO).

I would hold off the purchase until you hear back from Otto. You will be very frustrated if you purchase the property and find that it will not support the pond that you desire. Mike Otto is a premier pond builder and a great guy (quite funny to boot). He knows his stuff and will steer you in the right direction.

Will the Alpacas be "uphill" from the pond? In other words will this pasture be part of the watershed?

JHAP
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"My mind is a raging torrent, flooded with rivulets of thought cascading into a waterfall of creative alternatives."
...Hedley Lamarr (that's Hedley not Hedy)