The 2x4 bottom isn't big enough for a 10 foot span, but if you put a block midway, you now have a 5 foot span, which is ideal. Most people just use a piece of 2x4 for the block, which is also an ideal height for the bottom rail to be above the deck.
Your 1x6 top rail has my a little worried. Was that a typo or are you really wanting to use something that thin?
I have full 2x6 cypress boards and I was going to mill one down to a full 1”. So knowing that I can use the full 2”x6” for a top rail but it has to look good per the wife. The aluminum balust are 1” wide and take two screws on top and two on bottom. That should give support also