1) for initial application of O or O-A an Oz bank acct is OK.
2) on an O-A - for the first year multiple entries, after that a re-entry permit will be needed - each entry you get stamped in for another 12 months (hence on O-A you can get up to 2 yrs stay)
3) defo get an O-A in oz, you'll get 2 years stay on 1 visa. Otherwise you'll (probably) be on a 90day non-0 and then yearly extensions.
I'd say that if your from Germany and you didn't get a visa before you arrived in Thailand you're on a visa exempt entry (not VOA).
Such visa exempt entries can be extended by 30days at your local immigration office for a 1900บ fee, (and depending which immigration office you'll use you may need confirmation of your landlord / hotel submitting a TM30 notice).
This issue of comments disappearing after admin closed thread has come up before. It seems to depend on the version / platform your using as some people (me included) can view closed threads and all the following comments.