Tarantulas mainly are not regular feeders. Tarantulas can go for weeks without food because of their low metabolism rate. Weekly feeding attempts should be made. You should not leave remains from food or the enclosure may become infested with mites.
Crickets are the main food item or even meal worms.
Before a tarantula molts it usually goes through a binge and peerage period and then becomes very inactive so keep this in mind with young tarantulas. From my experience tarantulas mainly feed at night and this is when they become most active. The size of the water dish will depend upon the size of the tarantula. The dish must be shallow enough for the tarantula to easily climb out of and be able to reach over the edge. Submerging the dish into the substrate will allow easy access for a thirsty tarantula.