Hi Egon,
I moved from the US to France about 5 years ago. I also have e-trade, I just transfered all of my balanced to them, bank account, 401(k) rollover, Roth ... so now I only have one account for all of my US stuff.
After you move I think that you will have to send them Form W-8BEN Certificate of Foreign Status. I am not totally sure because your wife is American so maybe this does not apply to you. Anyway you better check. Once you sent the form, then they will withhold 30% of your dividends and send them to the IRS (I think the percentage varies depending on tax treaties between your country and the USA).
If you want to, you can buy vanguard ETFs in your e-trade account, that is what I do.
One quick note though, recently I have had difficulties transfering money from Europe to E-trade. It used to work fine but in the last year it has been annoying; I didn't really need the money so I managed otherwise but it is better that you know. Also remember that there will be quite a bit of fees when you transfer money (direct but also currency spread), ask around to see what is the best way to do it in Germany.