I would not set anything on the first 10-20 skills as they are normally used to define behaviour of entities via WED, probably not even on the first 90 skills.
What I normally do is to use skill100 as the global entity type skill, skill99 sometimes for subtypes and then use 90-98 for additional data/ pointers to reserved memory and the like (most other skills are used for arbitrary calculations and so on, depending on the function/ action/ entity).