Questions regarding new system

[TCArknight]

Howdy!

I am attempting to implement the CODA game rules from Decipher's Star Trek and Lord of the Rings games. I've made a little progress, but have a couple of questions on how to proceed..

I'm starting with the Star Trek rules, and these questions have come up:

1) How do I make an attribute (Psionics) hidden unless the character has an ability that allows it (Psionic Talent which allows the Attribute and starts at a score of 4 )?

2) How do I add fields to skills? I need to add a field that indicates whether a skill is useable untrained or Trained only, as well as one for making a skill fit one of four categories (Academic, Physical, Social or Psionic)

3) How do I hide Psionic skills unless the Psionic Attribute is visible?

4) In the CODA system, a skill can be:
a) The skill itself where the ranks are applied only for that skill. i.e. Empathy 3
b) A Specialty of a base skill and a character can have several specialties for a skill. i.e. System Operation (Helm)(Sensors) 4
c) One of a Group of skills, each individual and separate (But subskills of the same base). i.e. Science (Chemistry 4, Physics 2)

5) How do I calculate and display a modifier score for an attribute? i.e. Score of 1 is a -3 modfier, 4 is a 0 modifier or 10 is a +2 modifier
a) I'm thinking a script that pulls the final value of the attribute and assigns the modifier based on that score..?

I'm trying to get the basic information down for now... more in-depth creation questions wll be coming I'm sure.

Thanks!
Thomas