I found Hansa to be the easiest nation to form Germany as. You've got the money so just vassalise all you can and conquer/force annex the provinces you need.
Just take half of the provinces you need, hunker down and take the infamy on the chin (you can do this without going over the limit) then take the other half and enjoy those cores.
The problem with that is that you have to wait 50 years for all the cores. The reason so many are saying Bohemia is because with forced PUs, you can very realistically expect to inherit within less than 50 years, making it faster than even the speediest of conquests.