ricknroxy, welcome to the Winnie Owners' Forum. It is a great place for information and assistance. Here's a couple of thoughts:
1) for the King antenna, many times there are trees that block the satellites from the dish antenna so you might not want to permanently mount the new tailgater pro to the roof. That way you can move it to a spot with a clear view to the satellites. There are pros and cons to both approaches. If you do a permanent roof mount, I would remove the original King dish to re-use the wiring.
2) no special screws required but I would use stainless steel so they don't rust. The roof material is less than 1/4" thick so I'm not sure the screws really do much good. Most roof fixtures have butyl rubber tape/caulk between the roof and their mounting flanges. The sealant adds extra holding power. Some people use 3M Very High Bond (VHB) double stick tape as well but I have no experience with that on the roof.
3) as far as caulk to seal the roof, you probably will find thousands of opinions online about what is the best. I've been happy with Dicor sealant around fixtures and seams on the roof but not for the roof edge seams. I also don't use it to seal on the sides of the RV since it seems to get black streaky very easily. Winnebago does provide a sealant call-out sheet for their RVs in the Owner Resources section of their website. Here is a link:
A couple of other tips.
a) Consider creating a new thread if you have questions on multiple subjects. That way you can track each item individually without the thread getting all jumbled up.
b) Add a signature line with the information about your RV to make it easy for those trying to help you to know what you have.
c) And most importantly, go out camping and enjoy your new RV!