Re: novice builder
If the dust cover comes off easy, then it doesnt do anything but keep dirt out of the bearings,your coaster brake will work with or without it, but don't force it off cause on some bikes it might not be removable.
The dust covers i have seen were just a thin round piece of tin that comes right off easy. Most people either remove and toss the cover or grind the cover down so sprocket fits over it, the cover is like tin and easy to file down, the sprocket hole can also be made larger but is made out of heavy steel and has to be kept round or you will have sprocket wobble and chain loosening and tightening.
I'll let you decide which one you think you can do.