Unlock and upgrade is better buy max, stick to the later ones, once you get to higher numbers, the Reindeer and sled get far better return on investment than anything in the left column. Aim for hitting breakpoints every 100 as much as possible for your big earners. Reset whenever it makes sense. The buy is buying a girl's scene unlock. Each pair of girls you unlock gets you a scene (for example Alice and Lin, the Twins and Maggie). The price goes up with each girl unlocked. Girl 4 is already 100 Quintillion to unlock.