Your implants are in the process of settling in their position behind the nipple areola complex. a strap will help an awful lot applying gentle pressure in the right direction. the type of the shell of the implants shouldn't make a huge difference as to whether you should massage them or not
Choosing the "right" size implant is so subjective. Your surgeon can help with before and after pics of his/her similar patients as well as using sizers and imaging systems to give you an idea of what you will look like. My advice is to trust your doctor and remember that 25 cc is less that two...
If your nipples are above the level of the fold under your breast than a dual plane submuscular breast augmentation should round out the inferior portion of your breast and create a breast diameter that is more appropriate for your areola diameter.
