no flames - just thoughts.
one of the key things that led to successful events was to limit the driving times. 2.5 hours each way is a very long drive. i have found that more than a half hour and the attendance and participation falls off dramatically. most people just don't want to drive that much. when i did have a longer drive, it was always terminated at the next destination, and never came back again. factor in wine tasting and a meal, and you have some very tired people. also, putting a twisty run into the mix on tasting day is a recipe for disaster. this is the thing that has been wrong with all of the PCA events i have attended. they just don't get it.
a thought would be to start in one town, have a shorter drive, and then tasting, and then end at the hotel, get up the next morning, and end in another town, and a different hotel.
as for how many wineries, i was saying that an hour at each does it, but you have to add transit time, parking lot time, last minute bathroom time, etc. 15 minutes on each end of each should do it. 3 wineries would need 4.5 hours. that's why we would have a brief funrun, start tasting at 11 (can't drink wine any earlier than that) do 1 before lunch, and 2-3 after (depending on the wineries involved - boutiques take less time than big ones, etc). that would end us about 6. worked pretty well.
do yourself a big favor on the lunch. pre-arrange the menu, and charge in advance. if you get a big group, you can get lost in dealing with the ordering and paying. if you try to let people order, and put it on one check, and let them pay for "their share" you will get stuck with people who don't tip the required 25% for a big group, and you get stuck with the bill for the short. if you let them order separately, and pay separately, you spend a ridiculous amount of time dealing with it.
hope that helps.