Something that bothers me

If you are playing as Prussia, and conqueror all of Germany, and you form Germany, there is no point in doing so. Assuming this is your second run at this, and you already have the achievement, you have nothing to gain It is easier to just leave the HRE and become and empire, or stay in with your elector spot. A disadvantage of forming Germany is that you lose being the primary nation of a culture, and thus not all culture provinces have cores on them.