Hi, we are also booked into a villa in Plaka in June. From my research so far, it looks great for a family holiday- just as well as we're going with our grown up son, our daughter, her husband and 2 year old grandson. It's about 1.5km from Almirida, the nearest beach resort - a quiet resort with a sandy beach. About 4km away is Kalives which is a bit bigger and apparantly has all the shops you need. Plaka itself has a couple of mini-markets and tavernas, including one that comes highly recommended and I've heard good things about the food in Almirida. We are hiring a car for flexibility, as there are lots of places to visit from there, though I suspect our daughter and family will spend most of the time between the pool in the villa and the beach.
We know the area a little, as we visited Crete about 10 years ago and briefly visited Kalives. Chania is a must to visit, a fanastic place to wander round the little backstreet shops or eat watching the sunset over the harbour. The villa looks lovely, let me know if you go for it!