is_core = 46 # Mecklenburg
is_core = 50 # Brandenburg
is_core = 52 # Altmark
is_core = 53 # Lüneburg
is_core = 57 # Hannover
is_core = 58 # Anhalt
is_core = 61 # Dresden
is_core = 62 # Leipzig
is_core = 63 # Erfurt
is_core = 67 # Franken
Take into account that Brandenburg starts in a PU with Luxemburg so by 1415 they are bound to have a ruler with weak claims on the throne once their union breaks - allowing you to PU and inherit them. Brunswick, Luneburg, Mecklemburg and Hesse start with weak claims so they can be PU-ed right away.
I'd say this early amount of possible PUs premiums Bohemia heavily to do earliest possible Germany (they have the troops to enforce all the unions without getting annexed) but it leaves the problem of cultural shift in your hands. They also have +1 diplomat which makes all the RM/claim throne/declare war sequences much faster for them.
I say you start the game, start marching north on day one, RM Brunswick, Luneburg, Mecklemburg and Hesse right away, claim them all and PU as many as you can. Then wait until you can do the same to Brandenburg. Then you have to take Altmark and Franken by force from their masters and sit on 0.5 BB for 50 years waiting to inherit the rest.
Rush Gov 6 and build an embassy to mitigate it. Think you can just move capital to Berlin and flip culture once you inherit all of the above.
It's a shame you can't make Germany Vicky2-style if you have all the correct provinces PU-ed or vassalized...