You are about to be flooded with a huge tidal wave of conflicting opinions. Mine are simply the first.

"Which model will generate the most sales?" Simple. Look at what model has the most content here currently. Hands down it is V4. Bear in mind that Genesis and all permutations do not work natively in Poser, and the importer does not work well for some users (myself included.) Your sales to Daz Studio users may be good (if the item is good) but you will miss a fair chunk of the Poser market. Gen 4 content can be used natively by either platform.

"would a totally new stand alone creation sell better..."

Ahem.

Let me know how that works out for you.

There have been a number of new characters released the past few years, Hivewire's Dawn being the latest. None of the characters has met with anything approaching universal acceptance like Vicki 4. Dawn does have the advantage of having an actual company behind her, and many of us really like her, but the grassroots are still clinging to Vicki.

The issue with getting ANY new figure accepted is vendor support. That is to say, clothing items, hairs, skin texture sets, pre-made characters, shoes, etc, etc must be available and inplace the day the character is released. One of the things that has really hampered Dawn is that even in the face of initially huge vendor support, was that the morphs (dial sets allowing the user to create custom characters with the figure) lay undone for months. By the time they arrived, the initial excitement over the figure had died down.

Will a new figure get downloaded?

Yes, if it is truly well done.

Will it generate huge numbers? Probably not. Especially in the face of the number of figures that are given away completely free. You'd have to have something pretty special to crack that nut.

$.02