So I'd like to pull some advice from anyone about one of the disciplines for my Homebrew version for Way of the 4 Elements Monk. I have built this Homebrew version based off the impressive Remastered version by redit user u/SpiketailDrake and the version made by Nerd Immersion. So if you like this small preview of what I've created, please check out the original sources I've based my Homebrew off of and show them support. 

So I first need to mention, because it is relevant, that in addition to getting the options of Elemental Disciplines to choose from, in my version at 17th level you get a subclass feature called Mastery of the Elements which basically allows you to use each of the four 6th level Investiture spells once without spending any ki points and you regain the use of each after you finish a long rest. (pretty much the same as Nerd Immersion's version)

Mastery of the Elements

At 17th level you have become a true master of the 4 elements and have learnt 4 powerful elemental spells: Investiture of Wind, Investiture of Ice, Investiture of Stone, and Investiture of Flame. You can cast each of these spells once a day without expending any ki points and regain the use to do so after a long rest.

So what I'd like to ask peoples' opinions for is about this one 17th level prereq Elemental Discipline that I've written that is tied to the above subclass feature. Specifically I would like to know: Do you think its too OP? Do you think the ki cost is too expensive or too cheap? Is the wording too long or too unclear? Should I specifically add the names of the 4 spells in the description instead of referring them as "the 4 investiture spell"? etc. 

Avatar of the Elements (17th lv)

The ultimate form of controlling the elements, by combining all four into a powerful state. You can only use this discipline only if you still have all 4 uses of your 4 investiture spells from the Mastery of the Elements subclass feature. You expend all uses of each investiture spell as well as spend 10 ki as an action to cast all 4 spells at once, gaining their benefits and effects and being able to maintain concentration on all 4 spells simultaneously.

If you lose concentration while using this discipline, you can expend 2 ki points to lose the effects of 1 spell and have the others remain active. (Assign a number 1-4 for each spell and roll a d4 to randomly determine which spell you lose concentration for. Repeat if happens again)

Thanks