Welcome David,
To answer your query about OD’ing, since you are 20 you really don’t need that much of any pheromone since your body is producing a good quantity right now.
Ammo is good for club and nightlife situations and it is well buffered. You can not OD when using Instant Shine or Instant Openness.
You may also want to read This: Updated AndroticsDirect Pheromones for newbies
Good luck!