I am having a large gathering and I want to do a lot of the prep in advance. If I cook the meats, slice and freeze all of the above, then thaw in the fridge before making the sandwiches, will the flavor maintain itself?
Generally, freezing meat and thawing before consumption will not affect flavor. There are some precautions you can take when freezing and thawing to ensure that the meat doesn't get damaged (i.e. freezer burnt or overcooked if you thaw under heat). Here is an excerpt from a useful article on the subject.
When packaging meats for the freezer, the most important thing is to protect them from exposure to air. Wrap meats very tightly in either plastic wrap or freezer paper, pressing the wrapping right up against the surface of the meat. Next, wrap another layer of aluminum foil around the meat or seal it inside a zip-top freezer bag.
Packaged like this, meat can be kept frozen for at least three months. After this time, even well-wrapped meats can start to develop freezer burn, though I've often cooked meat several months after freezing and found it to be perfectly fine.
The best and safest way to thaw meat is to place the frozen package in the refrigerator and let it thaw gradually. Small cuts will thaw this way in about 24-hours while larger cuts can take a few days. If you're rushed for time, small cuts can also be thawed in a bowl of lukewarm water under running water.
For some more tips see the full article: http://www.thekitchn.com/freezer-savvy-the-best-way-to-freeze-and-thaw-meat-177355