DIY if you have basic skills and a saw to cut aluminum
These are not coated for outdoor use.
Yes you can cut top and bottom.
For ease of inserting into base and hand rail they give you a round top, if you keep full length. The square edge helps lock into your round hole at bottom to prevent movement with adhesive assistance
Yes. It is slightly smaller than the 1/2 inch.
Depends on the type of install. If the install is for new stairs, you could get away without a bezel or shoe if you install the balusters during the staircase construction.
The rectangle in the design is 2-3/4" in width and 20-3/4" in length.
You can go into the store and they will place an order with the vendor. But no, these products are not on the shelf in Home Depot.