Fun! I'll post a serious answer when I've more time; for now, some off-the-top observations:

• 1 AD is in the middle of Augustus' reign; the empire is in decent shape financially and is pretty religiously and culturally diverse.
  • So the hardest part of the God gambit is in getting people to pay attention.
• Roman politics included assassination, at all levels; extended engagement with Roman political life requires some safety measures, no matter how valuable you've made yourself.
• The German barbarians hadn't yet recovered from their losses in the previous century; provoking another great migration would be very hard.
  • And their religious practices were never well-documented, so boosting off of their existing structures is probably a no-go.
• Egypt might be more fruitful, I'll have to check.