It is best to bring money in travelers' checks what you will need for entire semester, if possible. If your parents must send you money while you are there, have them send a check in French francs. The exchange rate is better than for travelers checks, but you have to pay interest on cash advances.
Bank cards work in only a few places in France.
The 'Point Argent', found in most railroad stations, is the only ATM I know of that accepts American bank cards. Open a bank account only if you are staying for the year. Mme Desombre can help you select a bank in Tours. Since budgets vary so from person to person, we have no firm guide as to how much money you should count on spending during the semester. One way to estimate is to double what you normally spend here.