Because "use this ability..." is in brackets, it actually has no rules meaning - it's just reminder text. If you meant it to be a restriction on the ability, you need to have it out of brackets (and change "use" to "activate"). You've got a number of cards that do this.

That said, I'm not sure it's worth it; obviously you won't use the ability more than once usually, and it makes for good gameplay moments if you can pump this card's toughness and cheat some extra uses out of it.

Finally, Eager Cadet already exists.

Indeed. Similarly on Rabble Rouser. For reference, see how it's phrased on cards like Patron of the Orochi and Wishmonger.

I really appreciate all the feedback, it is a huge help. Comments duly noted and changes made.

+1/-1 is red. First strike, too, I guess, but white already has first strike, so it's weird that you need red.

the red cost is a flavour holdover from early in the set, there was a cycle of cards that cost one colour and had activated abilities that cost another colour. When I changed the R/W race from Minotaurs (Tren) to cats (Leonar) this survived.