You want your knee in the center with the brace like you and I have, many on here start and finish with these braces, some start with this type then graduate to a full leg adjustable brace, some start and finish with the full leg brace per Tom. I personally want to finish with the zimmer type brace like you have.
I go down the stairs backwards, like going up but in reverse, but I can't imagine going up or down with bilateral QTR's. What you have now is what you will have after surgery for six weeks, but with pain for the first few days. Get yr prescriptions filled before you leave the hospital. I would think you will be in the hospital for a few days or longer post surgery?
All the best to you Monday - Steve