Thanks for your report Bobbie! I'm sure it will be helpful to many -- and am delighted you had a good time. April indeed is a fine time to visit Santorini.
Your report on meals & prices may surprise many, but it reflects the difference in pricing between tavernas right on the main road, which are in small unpretentious buildings, just looking out at the road, and cafes & tavernas perched on the rimside. Another Firostefani handmark, Taverna Aktaion, actually is th OLDEST continually-running Taverna on the island (since 1949 I think) ,and it has prices just as good as the ones quoted... and it's only 30 feet from the Rim-path view, an you can see sunsets from its 2 patio tables. In fact, the have 2 tiny tables right against the path parapet; I have a photo of a couple there, silhouetted against the sunset.
Your advice about huge portions of side dishes is emphasized in every Greek guidebook I know... but then so few people read guides any more, they depend only on websites on their phones. Ah well. The reason for this is, Greeks traditionally would never think of dining alone -- they always find friends or relatives when mealtime comes. Thus side dishes are MEANT for sharing .. a Greek salad will serve 2 or 3... similarly, dishes of Gigantes (beans in sauce), grape leaves, french fries, etc. When eating alone, or when not very hungry, I have a tip for all -- in your daybag or knapsack, bring along some ZIP-lock bags! I learned that one eve in Serifos, on the beach. Wanted a lttle something before my dinnerplate, saw that olives cost only €2, and ordered -- and the plate held THIRTY-EIGHT olives. After eating a dozen, I found a zip-loc in my bag and took the rest home, for picnics. Some tavernas now are beginning to stock foam "clamshell" containers for "take-away" of unconsumed food, but it's still not common. To sum, the safest way is to order a few things, and FIRST see the food-volume that appears, and only then add to your order mid-meal if you feel you want more.