Nipple piercing corrects inverted nipples. They actually pierce just where the areola connects to it, not through the top part, this creates scar tissue that will make them bigger and erect. It can cause you to both gain or lose sensitivity in varrying degrees if good or bad. They are one of the longest healing timeframe piercings to get as the tissue is not the same as other locations and you go through a lot l more. They will also ve tthenost painful piercing you will get. Do both at once if you want both done or you won't be going back for a second time. The first one is a suprise, by the second you know what to expect. Prepare if its winter, you will be leaving a warm studio into a fridged outdoors, that will be like getting pierced all over again if you dont bundle up. Look into something like a soft breathable bandaid to place over them for the first few weeks as they will bleed and be very sensitive to chaffing. All this being said, best money ive spent, just make aure the studio you go to is know for more body modification/heavier piercings so that they are familiar with how to do it efficently and not have issue nicking a nerve or something.
As for the Septum, they dont pierce the cartalidge, it's the soft tissue just underneath, pull down your nose and feel it its right up front at the Nasal vestibule. Depending on the location and their licencing they may be able to pierce you around an 8 or 6 max, note this is more painful with more healing time. The main issue you will run into is the game of "holy shit I never realizes I touch my nose so much" and it will shock you. Hygeine is imperative to this piercing even more so, the area is known as the Triangle of Death for a reason, an infection is the last thing you want there. As for adding to sex, personally did not add anything but did not detract, other than when you both have them and get them caught together. They are easy to hide, you can flip them up into your nose or just but a skin colored silicone bar for while at work (once it has healed). Being led around by it is not something id recommend, its a very soft fragile area of tisaue and can easily be ripped out with minimal tension (under 15lbs of torque would be sufficent) so do with that visual as you will. I feel septum piercings are much more normalized and common plave now so people have less aversion to them in the work place but YMMV.
Hope that helps!