T.C.
Hi,
Great questions. When you cook a casserole, like lasagne, you would want to pull it out the day you plan on cooking it. Then, you just heat it until it is warm. The caution of putting it directly in the oven from the freezer would be if you have a glass pan, you want to preheat the oven with the casserole in the oven so that there isn't a huge thermal shock. It should already be cooked fully before you freeze it, so warming it is all you are trying to accomplish in the oven before eating.
Meats can be frozen for about a year (depending on how good your freezer is) before cooking and eating them. The exp. date is for fresh meat unfrozen before consumption.
I would not cook the vegetables before freezing. They will lose more nutrients that way. Just freeze them and cook when ready. If you can, you might put them on a cookie sheet to flash freeze them first. Then, put them in a freezer bag to freeze them. This way, they won't all stick together when you want to get some out to cook (like bags of corn, peas, etc.).
Enjoy your freezer!!
ETA: I forgot to mention that you can also cook meats, like ground beef, before freezing. Then, put them in a freezer bag to freeze. When you need a quick meal, you have cooked beef already to go. You can add seasoning (taco) or sauce (spaghetti), and you have a meal ready. It's quick and much better than store bought fast food.