If I buy a die do I also need the handle and all of the other parts?
If you buy a tap and die set it will come with one, however most sets don't come with a UNEF die. You also can use a thread file which will have a side with a 28tpi file on it. Typically you use this in a lathe though as its much easier to take off an even amount when the barrel is spinning and the file is stationary not the other way around.
You might be able to sneak up on it by hand if you back the tension screw out and the screw it in little by little with just enough tension that you can still rotate it by hand. Hopefully they went with 1/2x28 and not 1/2x20
This small fix would add up to $25+ because I don't have the tools.
Your call . . . personally I like having a bunch of tools even if I only use them 1-2 times a year.
Called a local gunsmith I have worked with before and they would not try the die on the end
Find a new gunsmith.
You can get carried away on a die and undercut them but the thread form already exists for what you are doing and theoretically was cut when the barrel was made with the intention of being perpendicular to the bore. Secondly, the primary aligning feature a thread-on silencer uses is the shoulder just after the thread relief not the threads.