Re: Who's eligible to teach Aikido? And what level a sensei should be?
Inasmuch as you don't know anything about Aikido, learning about it from a shodan or nidan shouldn't be much of an issue.
More important than high rank is the ability to teach well. I would rather learn Aikido from a nidan who was an effective teacher than from a godan who was not. Also, it is a mistake, I think, to assume that, because one is highly skilled at Aikido, one is necessarily highly skilled at passing on that same ability in Aikido to another. O sensei himself is a good example of what I mean. He founded Aikido but was not particularly successful in replicating his martial ability in his students. As far as I'm aware, none of his students were ever as powerful as he was.