So there are a few suggestions I could make but I have a few questions. Why are you concerned over how often you increase or decrease statistics? Is it to make checks that are fair? If that is the case, I would recommend a few things to potentially make things easier.
If you know roughly how many skill lifts you wish to have, then you can figure out how many you plan on spreading. For an example I will stick with 18 lifts of 5. This allows you to start with any score at 10 at the beginning of game. With this you know that you will never break a 100 score even if they focus everything into one skill.
From here you can make a variable that you lift whenever you lift skill. For the example I’ll call it LiftTrack.
With these set up whenever a stat is lifted you just add code for *set LiftTrack +1 to track the amount of lifts you have.
You can now use this lift tracker variable to judge how difficult the check should be. Using a range from 1-5 you can now set how hard a check should be. You can set variables in your start up to allow you to shift what these difficulties are throughout the whole of your story.
In the start up you can do this:
*create Easy 1
*create Normal 2
*create Challenging 3
*create Difficult 4
*create Evil 5
*create LiftTrack 0
So that when there is a check you have code that looks like this
*if Deduction >= (LiftTrack * Difficult)
Stuff Happens
*if not(Deduction >= (LiftTrack * Difficult))
Failure
So lets say that there has been 3 lifts total. That means that formula looks like this once the numbers are plugged in: Deduction >= (3 * 4).
Turns into Deduction >= (12).
Meaning they would want a 12 or higher to succeed at the check, but might have a skill as high as a 25 (Base 10 and three lifts of 5 each)
And an evil check would math out to: Deduction >= (3 * 5).
Deduction >= (15).
Making it very hard to pass if the skill never started with that base 10.
The real magic to this approach is when you are testing, if you feel that all of the normal checks are too easy or hard in general, you can just change the variable Normal in the start up and it’ll fix all checks marked as Normal. The same goes with Evil or Difficult, you can lower them to more feasible numbers.
This method though encourages players to focus really heavy in one skill if you use a lot of 4 or 5 ratings for difficulty. You may want to keep those super high checks be very sparse or never have them happen. Instead define Evil as never higher than 3.75 or something.
Please let me know if I confused you at all in this.