Going after the Allemanni is probably sensible from a gameplay point of view. The ERE can wait - they are often targets of the Vandals and Huns, so taking them on early may merely transfer that problem to you.

If you get all of your starting towns under your control and build economic stuff (ports & mines), you should have no money problems.

But with a -12500 balance, you might want to think about immediate cost cutting - scrap all foederati cavalry and your navy. For a cash infusion and to secure your borders, exterminate the Celts, Berbers and Allemanni; maybe scrap a few low grade training buildings.

I can't see scrapping churches as cost effective - it will cause loyalty problems and you'll presumably have to spend more to build pagan alternatives. But maybe I'm missing something.