Your faction trait means that whilst you're free to change religions if you want, there is a benefit to keeping one that is different from your neighbors. armies of other religions) makes these early game fights much more manageable, especially if you've got a few clubmen to hold the line. If migrating, you can opt for the warmer climates though I chose to head up to Britain.
Not to mention the Huns like to show up pretty early on and make a mess of things. I'd honestly recommend migrating because even though it's pretty easy consolidating a foothold in Germania (your starting army can take out the Thuringians or the Alamans on the first turn), there are so many rivalries at play around you that you'll end up fighting wars on many fronts.
The first thing you need to do is decide if you're going to stay in Germania or migrate elsewhere. Thus far the campaign that has held my interest the longest has been the Langobards, so I'll write a quick bit about them