Design Notes:
- I based most of the point costs on the point costs given in the OP's initial post. I increased the cost of the attack bonus because that seemed like the one everyone seemed to want.
- The purpose of the diminishing returns for both "buying" and "selling" CMs is to make "min-maxing" less likely and diversity more desirable. (It's effectively the same reason why the ability score point buy has diminishing returns.)
- I added the "3 Related Skills" option because it seemed to fill a gap between the one skill and all skills options. In the OP's system, if you wanted more than one or two skills to have bonuses you might as well just buy all skills.
- The rules for combining individual skills and "all skills" packages may be a little confusing, but it was the only thing I could come up with that was logical, fair, and not easily exploited. The way to think of it is that if you get, say, +2 to all skills, the +2 is the "base" that you've already paid for if you want to buy more for a particular skill.
- The reason you can't get a penalty to an individual skill or 3 related skills is because otherwise everyone would just take big penalties to skills that they didn't plan to use in order to get lots of points to put in other. Also, they could get lots of free points by say, getting +4 to all skills for 12 CP and then selling back all 17 of those skills one at a time for 3 CP each.
- Initiative has a very low "sell-back" value because many characters have little use for initiative, for example back-line characters like wizards and archer rangers that aren't usually the first into combat and often want to wait anyway to see the enemies move up before they attack. These characters would almost always want to sell back as much initative as they can for points if the value was higher.
- I based most of the point costs on the point costs given in the OP's initial post. I increased the cost of the attack bonus because that seemed like the one everyone seemed to want.
- The purpose of the diminishing returns for both "buying" and "selling" CMs is to make "min-maxing" less likely and diversity more desirable. (It's effectively the same reason why the ability score point buy has diminishing returns.)
- I added the "3 Related Skills" option because it seemed to fill a gap between the one skill and all skills options. In the OP's system, if you wanted more than one or two skills to have bonuses you might as well just buy all skills.
- The rules for combining individual skills and "all skills" packages may be a little confusing, but it was the only thing I could come up with that was logical, fair, and not easily exploited. The way to think of it is that if you get, say, +2 to all skills, the +2 is the "base" that you've already paid for if you want to buy more for a particular skill.
- The reason you can't get a penalty to an individual skill or 3 related skills is because otherwise everyone would just take big penalties to skills that they didn't plan to use in order to get lots of points to put in other. Also, they could get lots of free points by say, getting +4 to all skills for 12 CP and then selling back all 17 of those skills one at a time for 3 CP each.
- Initiative has a very low "sell-back" value because many characters have little use for initiative, for example back-line characters like wizards and archer rangers that aren't usually the first into combat and often want to wait anyway to see the enemies move up before they attack. These characters would almost always want to sell back as much initative as they can for points if the value was higher.