title_body: How can I keep several pots of coffee warm?
upvoted_answer: Actually, this answer will eventually boil down to the forecasting of time dependent expected coffee consumption function of your guests.
  
  You may expect that, right after a meal or right after they are seated people tend to drink coffee all together at once. Therefore, it is better to keep most (all?) of the pots filled up when you encounter them at first.
  
  Then, the servers may check the pots and replace the most crowded tables' pots with empty tables' pots for a while. During that time, you may prepare your second tank of coffee brew.
  
  To keep the coffee fresh, you may preheat the water, I assume. I'm not sure if your percolators are compatible but you may just heat up the water in the big one. Then use the smaller ones to brew smaller batches of coffee to keep rather fresher and smaller batches of coffee. Also, if some of the coffee remains, it is clear that a smaller batch will cost you less.
  
  Besides, for serving decaf, my approach would be something like that: I would keep a few of the servers busy with serving decaf around the less crowded tables and only leave decaf pots in the most crowded tables. (Assuming that decaf will be consumed less.)
  
  All and all, all of the above is my humble opinion.