Sounds good, bro. I can't stress enough to BE CAREFUL WITH THE M105 That shit is deadly, 100% liquid sandpaper and will strip clear coat in minutes. I can't imagine you'll need it on the Mustang.
I am not planning on using the 105. I wanted to get it, just in case. It comes with the kit I bought so it worked out well.
I don't believe I will need anything more than the 205 but it doesn't hurt to have the 105 and not need it.