Hey ya! I have an idea for the Custom Item Stats Simple system. I'll give an example for giving MP. You will need 4 abilities, each with 9 levels. The first one increases mana by 1,2,3...9. The second one increases by 10,20,30...90. The third one : 100,200...900. The fourth : 1000,2000,3000...9000.
You see where i am going? When the user defines how much mana he wants to add, you do this : convert the real variable that holds the mana amount to a string. Then get it's string length. If it's 1, then you use the first ability (which is for units). If it's 2, then you use the second ability as well (which is for tens). You see what i mean? I'll give an example.
The user wants to add 114 mana :
1. Give 1st ability (for units) to the unit and set it's level to 4 (in this case)
2. Give 2nd ability (for tens) to the unit and set it's level to 1 (in this case)
3. And then the 3rd ability (for hundreds) to the unit and it's level should be 1.
It should be better, i think.