I think you need hands on professional help to get your project out the door in good shape,
It's one thing to get rough numbers to shoot for in order to get in the ballpark, it's another to actually know what you're doing (and thus know why you're doing it, versus just doing something because you've been told you should). For example, you can get intersample peaks above 0 dBFS when peaking as low as -3 dBFS (one could argue as low as -6 dBFS as was demonstrated by the TC Electronics team who wrote a well known white paper on the subject). A professional mastering engineer knows how and when intersample peaks occur, on what devices, with what type of material, what kind of distortion they introduce, etc. Depending on the genre, the audience, the distribution scheme, the loudness requirements, and many other factors, he can then make an educated decision.
Now I do understand that not everyone has the budget for a professional job, but make sure that you're aware that just shooting for any kind of specific numbers on your meters is not a guarantee that you're going to get the best result.