Chile Con Queso

If it's just cheese, milk, and chiles, I would prep all the ingredients (shred cheese, chop chiles) and mix in a crockpot the night before and then cook in crockpot a few hours before the party. For most recipes you are just melting the cheese and adding the chiles and seasonings, so why not just do that in the crockpot the day of.

Here's a recipe for essentially a cheese sauce that you can turn into chile con queso by adding the chiles, http://www.seriouseats.com/recipes/2010/09/cheese-sauce-for-cheese-fries-and-nachos.html

It has instructions for reheating in the microwave which to me says that you can make it ahead of time and reheat, even in a crockpot.

Are you speaking of the mostly cheese dip that contains chilies, onions and sometimes tomatoes? If you are making the American version with a brick of Velveeta, yes. If you are making the authentic version with white Mexican cheese and milk, I'd worry it may separate. I'd just make it the day of to be safe.

Yes. Chiles like most stews actually taste better a day or two after cooking because the flavors meld together. Many soups are like this, too.

That said, it is typically best to add the cheese or other dairy before serving (and only to the portion that is going to be consumed immediately). This is in fact what restaurants do: finish to order.

Ratatouille and caponata definitely fall into the "better the next day" category.

As a plus, you will save yourself some time on the party day. Good luck!