A Common practice is to use Fatigue as a "secondary" stat to Strength, where initially Fatigue is equal to Strength. Additional points of fatigue may be purchased at the rate of two points of Fatigue for the number of experience points that would be spent normally to increase a regular attribute one point.
Likewise, Skill/Spell Points is handled in the same fashion, using IQ as the base. You may choose to spend the points immediately, or, in the case of skills, save them up to purchase a more expensive skill.
When calculating "level" for XP requirements, factor back in Fatigue and Spell/Skill points (SP) at the rate of 2 to 1, or it is easy to use the formula below which takes it all into account)
Effective CP = (Str + Fatigue + IQ + SP + 2*DX)/2