I tend to pack up and ship out of initially poor and underpopulated Germany and begin a new wave of Völkerwanderung. Seeing as there can only be 'one' Empire, I head to Cornith and conquer north and east until I hit Constantinople/Niacea and you can do this with your starting units if you have skill on the battle map.

Note: Be sure to make lots of alliances and milk money out of your neighbors for trade rights and map information before leaving Germany. You need that cash when you let Germany rebel away or gift it to the Pope (or both).

Initially, you are very isolated and not exactly in a defensible position, as Hungary will have Sofia by the time you get there and Venice is always threatening from Ragusa, but with some patience and skill you can gain those lands for yourself and settle in. Venice tends to give me nothing but grief so I have to eliminate them (damn suicidal AI) but after that things seem to quiet down. Hungary will continue to play around with you because of Sofia but with your excellent castle units you can deal with them. I hold for a time in the west and focus on the east with both agent and military conquest.

Pros: Wealth, faster access to high end units, easy Crusades and easy access to non-catholic foes. Oh, a pro for enjoyment is watching the power vacuum in Germany.

Cons: Initial difficulty (one shot of bad luck and you could be done), extreme poverty before you take your new homeland and strange AI behavior (seems they don't cope well with the HRE in the Aegean littoral).

Give it a try. You'll have fun, win or lose.