Re: Safety amongs beginners
I think it's good that you've talked with your sensei about this, it's the first thing I would have suggested. If you are seriously worried of getting injured I think it would completely ok to not train with this person until you're a bit more experienced, let the advanced students work with him who can handle it. As to other people getting injured, I think that's your sensei's responsibility. As long as he is aware of the situation.
I hope your aikido experience so far has otherwise been an enjoyable and positive one!