Are we talking about the same Aizen here. First off all what do you mean he wouldn't risk hollowfication, the very reason he did all of this is to acquire the abilities of a hollow so ofcourse he would do it. Its just that until the Hogyoku there was no way to do it without just completely becoming a hollow which is why he was doing research to find a way to accomplish it.

Secondly Aizen doesn't want to become a hollow or a vaizard, what he wants to do is completely blur the lines between the two so he can have the power of both. Hollowfication, at best, would only turn him into a vaizard and that is not enough for him because even though thus far they are the closest thing there is to what Aizen truly wants you can't possibly consider being a vaizard to be an ideal situation, because not only do they have to wear a mask to access their hollow abilities but they can't keep their masks on indefinitely and the mask can be broken and there would still be the constant threat of loosing control of your inner hollow and becoming a true hollow.

I don't even know where this pussy comment comes from. Aizen has always seemed more than willing to fight anyone but he just doesn't seem to be the type to waste his time on someone he deems unworthy if a subordinate could accomplish the task and we've already seen him have his way with captain class shinigamis. The only time I've seen Aizen run from a fight is that one time on the execution grounds and I wouldn't consider that running since the only reason he was still in SS in the first place was to get the Hogyoku and once he had gotten it, there was no reason to stay.