I'd just give it a try and see if it works on a spare piece of wood
You can call the Milwaukee Rep. at your local Home Depot.
Take it back to where you bought it, should be a Milwaukee Rep. who will either replace it or tell you what you need to do
I'm not sure why the set screw isn't coming out, try inserting your screwdriver into it and give it a slightly harder than usual tap. If that doesn't work, return it to where you purchased it
I'm not sure about the warranty. What I do is take my Milwaukee tools to the rep at the store to see if there is anything he/she came do for me. But usually with bits, drill attachments, etc They usually won't cover it unless its brand new.
Yes, I use it on my 5" and 6"
Nope. You need a 1/4" quick change shank
See the Milwaukee rep.
Good question, Yes . I used with a 2" Carbide saw.