How do I know....

[Gary Rushworth]

When my players are due to get another * and how do I do this quicker.

[Buffs Mad]

When the average of their 3 attributes is the next multiple of 5.....

It takes 5 sp to raise 1 attribute grouping (def, att or phys) by 1.
It takes 15 sp to raise the players (average) Q rating by 1
It takes 75 sp to go from having just gained 1 star to the next 1.

So just count in 5s.