Regarding the account approval, the question I would ask is who do you turn down and why? If you don’t have strict enforcement standards, there probably isn’t much of a point in doing this. It might result in a faux feeling “safeness” but isn’t really stopping those from viewing content that we’d rather not view it.
Again, unless there is some rationale and process for strict enforcement, I would pick 3.a. This should allow the content to be more easily crawled; it would make it clear to all that this is an open site, and would allow far more participation from those interested.
The gamble you in effect are making is that you can control the spambots easily enough, and that those interested in participating are really the only ones who will hang around.