Hazmat
So far, it looks like you are getting your questions answered. Level on the frame is the way I went, and adjusting the chain on the lift cylinder is what I do to get the up and down travel correct.
Other things to consider: May have to install some flow control orifice in the lift hyd line to slow the lift down. That is something you will learn after you get your plow hooked up.
When laying out the location of the plow, take into account the location of the plow when angled, and the location of the front tires when they are turned all the way (right or left). My original design had a conflict, and I learned about it before the welding began.
The springs on the plow are balanced right, although I added two springs to my previous plow to keep it from folding too soon. I wanted more dig. The Western I have now is good with the springs that came with it.
I have the short A frame, not the standard one. It keeps the plow closer to the front of the tractor. Before welding a bracket, I would suggest you have the plow first. A narrower plow and A-frame may not work the same as a different plow (noting that you are thinking about a smaller plow).
Your design looks good so far. Wish I had the CAD program to use when I designed my bracket. Instead, I fashioned one out of wood, gluing the pieces together for a mock-up that I could try on the plow before taking the mock-up to the welder.
Good luck on your plans. You will really enjoy the blade out front, compared to the blade on the back.