As regards studio stock photography, It would be quite hard to take more than a half-length portrait photo with 135 or even 100mm unless you have enough room to step back. For example, with a 135mm which is mounted on a FF body, you will take only a tight head shot in the distance of 8-10 feet which is normal in a studio. Moreover, in your field, it is also required to illustrate context and circumstances through which your photos get their meaning.
With an 85mm lens, at the same distance of the former 135mm shooter, you can take a proper waist up portrait from a average-height person. Therefore, I suppose that choosing between 85mm L or non-L is not the matter. First, you'd better to find the best focal length suits your field more.
And, if you are going to buy a 70-200mm in the near future, why are you still looking for a 100 or 135? It will cover most of your portraiture work very well, I bet you!
So, you have two choice: 1) "70-200mm F/4 L IS" as the first lens, or 2) 85mm or wider and 70-200 in the future.
Finally, I would say that the advantage of a wider 85mm lens is that if it was too wide, you would still be able to crop the photo and moreover, closer you are to the subject, shallower depth of field you achieve which enhance your photos considerably.