You can probably go pretty big, but whether or not that is truly advisable is something you'll have to discuss with your PS.
First, though, from a technical standpoint, it LOOKS (from the photo) like you can have a reasonably large implant. A lot depends on things I can't see from the photo (how much extra skin you have, how thin it is, etc) but it looks like there's enough to have a fairly large implant. At least some kind of D, although I don't know if you can go to an F right away. You should also be aware that cup sizes vary from manufacturer to manufacturer - a Victoria's Secret D might be someone else's C - so try not to be too fixated on a specific size.
What I try to advise my patients to do is to choose an implant that will look right on them. There is obviously some wiggle room there, but the larger the implant the more it will look "implanty," and the larger the implant the greater the potential for perioperative complications. Factors such as excess skin, how broad the shoulders and chest are and how tight the tissues are (they tend to be looser if there have been pregnancies or weight gain/loss from any reason than in younger patients and/or those who have always had very tight skin). Bringing some photos of the results you'd like can help you and your PS make a decision as to what size will come closest to giving you what you want while, at the same time, minimizing the potential for any problems.
Also in general - silicone gel implants look and feel softer and more natural than saline implants do, although there are many exceptions to that and some of that also has to do with the percent of filling of the saline implants (the less they're filled the softer they'll feel - but they'll then also be more likely to be associated with rippling that can be seen and felt, particularly in thinner women).
In short, there is no absolute answer to what you're asking - but I think that you can get an excellent result with a single procedure and I would, in general, aim for a nice, realistic result with one procedure rather than been dead-set on a specific bra cup size.
I hope that this helps, and good luck,