The following is in no way meant to be insulting or hurtful. I am just stating the facts that i ran across which rubbed me wrong. This may sometimes be very blunt but its only to make sure we are on the same page.
Well were should i start Patrick,
First of All: I doubt that Onyx can be worked into a Armour much less so into a Plate Armour. That is if we assume you mean the stone. If you mean the Gem than the sheer amount neded would be impossible to procure.
The next point is that such an armour even if it was possible to craft it would weigh far too much for any human being to carry. It is simply impossible. Not to mention that such an armour could be easily shattered. Take any kind of stone that is about as thick as a plate armour (which is about a few milimeters thick) you can break it apart in your hands.
Continuing on to your bow: We are in a Medieval timeset i doubt they had anything like a compound bow back then...maybe you meant a composite bow?
But we are not at the end. His Onyx Bastardsword while propably the only thing your character ones which would be possible to produce in medieval times would shatter upon impact. There is a reason people never used swords made of stone. Daggers yes, as sacrificial tools. And though it is said that Aztecs used Obsidian Swords, these were made from wood and Obsidian was added on the edges.
But lets ignore the simple matter of your Equipment for a second, lets assume instead of onyx plate armours they have plate armours out of normal iron or steel.
think for a moment 700 men, after your own description the best you can have for money, plus 700 destriers (propably closer to 1400 because you need spares) and their equipment (steel horse armour, plate armour, bastard swords, replacing your compound bow here with crossbows).
Take your whole glorious detail and now imagine how much all that stuff would cost. Now look at the map and read the Starting Story again. You are surrounded by poor and impoverished kingdoms with the notable exception of the Darkbrook Shogunate and the Theocracy of Mourn. Both of these who would be able to afford your detail wouldn't do it because they (in the case of Mourn) do not hire Mercenaries or (in the case of the Shogunate) won't buy your detail because for the same money the can get 20 times your number which is more useful to defend thier vast borders.
In other words on the entire map is not a single person able or willing to afford you at the beginning.
And finally i have complaints about your character. While i am sure you put lots of effort into him i can' tput it any other way but this: he is an utter and complete Mary Sue( if you are not sure what a Mary-Sue Character is have a read
here , especially note the part about Cliched Character).
While ther eis nothing wrong with a Character with a Tragic Backstory yours is completely over the top and has reached a point where it isnt tragical anymore but has reached a comedic state. The whole description of your Character makes him a one dimensional figure for which we should feel emotion and hope that he makes better after so much tragedy but all in all i already don't like him. the whole description screams of the Dark Knight or Warrior Poet lamenting over his misfortunate lot in life while fighting the good fight, as a Mercenary no less.
All in all while terribly romantic such a character is one-sided,bland and seems utterly unreal. Correct me here if i have assumed wrong.