Good on you for rescuing the poor guy. It sounds as though you have done wonders for him already. The foods that you have mentioned are fine, although I wouldn't overdo it with the lettuce as it has very little nutritional value. Any of the brassica family are good to feed as are tomatoes and nasturiums.
Tortoises will drink water if it gets very hot but most of their moisture is derived from the foods they eat. However, always keep a shallow bowl of water handy for him just in case.