Unfortunately I cannot give you the answer to your question: it is impossible to say a priori how much water the tomatoes need. The climate of your area, the type of soil you cultivate and many other variables significantly change the amount of water needed. You can find some useful criteria on irrigation in the article dedicated to when to irrigate the garden, now I can only give you some general suggestions, but not precise quantities because those depend on too many factors related to your situation. Mulching is a great idea, it helps the soil stay moist and reduces the need for water.
When tomatoes need water
The first thing you need to know about tomato irrigation is that there are times when water is particularly important. The moment in which the seed germinates and the seedling has to develop is to be taken care of with great attention: the young plant has slender and short roots, therefore it is not able to search for water in depth. For this you need to irrigate regularly and never let the soil dry out. Even when flowering begins, more frequent irrigation is useful, since fruiting involves a greater waste of water.
Wet little and often
Irrigating tomatoes is very useful, but you should also know that wrong watering is also a major cause of plant disease. Tomato diseases, such as downy mildew, fusarium and gray mold, in fact proliferate in excessive humidity. In particular, when temperatures are mild, excess water must be avoided. For this reason, it is better to bathe rather frequently but never overdo the quantities of water. Furthermore, the leaves should not be wet but always the soil near the stem.
Recognize watering errors
If you irrigate too little, you can notice the suffering of the plant, so it is necessary to intervene by wetting more often, but without excess. Too much water can also cause problems, it is one of the possible causes of apical rot in tomatoes. Also in this case, if you notice the problem, you need to reduce the water intake.