I would want more than 5 gallons of tank at the top, because if you are lugging two five gallon pails, you will want to be able to splash both of them in and head back after more sap while they drain through. You also ought to have a screen or filter in the top of your dumping station to catch the ice chunks, the right piece of ice (or bark) could plug up your whole system.

So on the days when it runs well and you gather 2 gallons of sap per tap, you are going to fill one 55 gallon drum at the bottom of the hill long before you collect all 100 taps. I would plan for 250 gallons of storage in that case myself.

Once you drop off that hill, the pipe run nearly level for a good distance at the bottom, perhaps a two percent slope so it would drain and not freeze. I would be tempted to get the sap across the ravine by pipe rather than cross it with that atv if that is possible.