RMMV Damage Formula - ideas and help

The gist is, using Yanfly's Skill and Damage cores, to modify the cost and damage formulas of skills based on certain variables. This would allow for a user driven skill upgrade system. For example, if a character has 100 JP, they can upgrade a skill one level and increase the damage output while increasing the cost. To elaborate, consider this simple formula:

a.atk*5 - b.def*2

Simple, right? It could be upgraded to do more damage, like in this way:

a.atk*5.5 - b.def*2

Which would make it do 10% more damage overall. Meanwhile, the cost of it could increase too. And then you could upgrade more times, say a maximum of 5, until it is doing 50% more damage over the original, which would be:

a.atk*7.5 - b.def*2

Anyway, here's the key point, which I'll emphasize for clarity:

Rather than clogging up the skill list with multiple copies of each skill, varying only that little bit, I want to be able to put it all in one massive (and ugly) notetag, with each one taking effect based on a variable (the skill level) that the user has control over.

For example, I'm envisioning something like this, except actual code:

<damage formula>
if (skill level = 5)
a.atk*7.5 - b.def*2

...

if (skill level = 2)
a.atk*5.5 - b.def*2

if (skill level = 1)
a.atk*5 - b.def*2
</damage formula>

And then do the same thing with the skill costs, maybe increasing by 10% each time or whatever.

If I'm not mistaking anything, this should be doable as I described. And I can think of some other issues, but I don't want to get TOO off-topic, as I feel I'm already pushing it.

A post I saw on here at one point, but cannot find, referred to a game where you could use stat points to boost attack power. This gave me an idea. I was planning on implementing a dark knight character into one of my games, but the standard version is slightly dull. The standard version, if you don't know, sacrifices health to deal extra damage. This is an interesting twist that could lead in some neat directions. For example, instead of sacrificing health, sacrifice 10 of your ATK stat to deal massive damage to an enemy, or even a whole level to clear out the field. The implementation is similar to the first part, using the damage formula plugin to use those stats as costs. I THINK it should be possible, but I'm not sure how, and that's what I'm asking here.

To build specifically off of my examples, consider these formulas, which are ones I'm considering:
<damage formula>
if ATK is greater than 100
subtract 10 from ATK
a.atk*10 - b.def*2
</damage formula>

Or this one, the level one that clears the field:
<damage formula>
if level is greater than 50
subtract 1 level
b.hp (or whatever will deal damage equal to all enemies current HP)
</damage formula>

The advantage to that second one is that you could give it a unique element, and then make bosses 50% resistant to that element, which, if I'm right, should cut their current HP in half instead of outright killing them, still making it useful against bosses without being broken. But I'd need to test that, and I'm going to bed right after finishing this post.

heal=(200+a.mat); a.gainHp(Math.floor(heal*.2)); heal; // this works just fine in the damage formula

<Post-Damage Eval>
var heal = Math.floor(value * 0.25);
a.gainHp(-heal)
</Post-Damage Eval> // this works just fine in the notes

The problem I'm having is that I need the caster heal effect to be activated conditionally. ie. when a variable is equal to or higher than 19

My scripting knowledge sucks massively, so I'm probably just doing this wrong... but if anyone can see the obvious solution that would be ace.

I'm trying:
v[5]>=19 ? heal=(200+a.mat); a.gainHp(Math.floor(heal*.2)); heal : (200+a.mat)

(Math.randomInt(20)+1+a.atk) > (10+b.def) ? Math.randomInt((8), 4)

if (b.def <= (Math.randomInt((20), a.atk) +1; ){ Math.randomInt((8), a.atk) +1;} else { 0 }