You can use as many TS in a day as you want and as many CS in a day as you want. You can even not use any in one day if you choose. If you are staying 4 nights then you have 4 TS, 4 CS and 4 snacks for each person to use during the 5 days you are there. Use them all the first day if you'd like. The meal credits are on your room key as well as your park passes. The total number of credits for your party are available from each card - you just have to present one card to pay for the meal. A 15% tip is included however, you may leave an extra tip if you think the service warrants it.
As for using a TS for a CS, yes it can be done, however a manager at the restaurant will have to process it for you since the computer is set up to remove a CS credit from your bank of credits and will need some sort of override to remove a TS instead.