I'm not a stickler for length of a backstory. A good way to get some finer details down is by asking a few core questions.

What events turned them into who they are?
What personal stakes do they have from the events?
What drives them?
What traits did they acquire along the way?
Scars, [i]missing arms,[/i] what story do those tell?

A thing that I noticed is that you explained away your skills in the capabilities. You could instead use the backstory to explain how they have what they have. 

I'm not looking for exact details. More along the lines of justification to who they are. You can heavily imply things that you don't want to tell.

But it's looking good so far.

And JUST IN CASE, you will have a few days more after the IC goes up because weekly posts. Tho it would be good to get it in sooner rather than later.