I would do a single large unit first, and don't upgrade the pump to oiless, they been having problems.
Before you buy a FD though start working with mylar bags and o2 absobers. Instead of a 2nd freeze dryer I'd get a nice vacuum chamber sealer.
Find and old brita filter pitcher, yank out the charcoal filter, and stuff TP rolled up tight in the hole, makes a great oil filter, which you need to filter the pump oil every batch or every other depending on the food.
Prefreeze everything in a -20 freezer before you freezedry, eliminates the vast majority of issues people have with foods expanding under vaccuum then drying into a hard lump - epic mess, looks like a bomb went off, but if its frozen rock hard it'll hold up better when the intense vacuum is applied.
Enough vacuum to boil cold water.
They're neat, it'll take ahwile to make it pay off.
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