Also, I would cook the shells very al dente and sauce the bottom of the pan well before placing the stuffed shells in the pan. This will prevent them from sticking and it's fine if the the shells are al dente and absorb some of the liquid. The flavors will meld and develop overnight and it will be great the next day. I happen to think most Italian dishes taste better the next day and that goes for pre-prepped dishes like shells, lasagne & other baked dishes. As long a the pasta is not over cooked, the dishes hold up quite well. Without any sauce in the pan, the shells are likely to dry out in the refrigerator overnight making them very chewy once they are baked.
FWIW, I am 1/2 Italian and learned to cook from my off-the-boat Italian Grandmother/Great Aunts.
Buon Appetito! 
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