Were it mine, I'd consider having the one single railing on the right side, and on the left side I'd have either the existing two segments of railing or remove the upper section along the wall as no longer needed. Re the left newel post being too tall, I think the installer needs to verify that the railing height is adequate. The railing appears too low to me. I am not sure you understand the complexity of the installation nor the costs involved. I am of above average handyman skills, but I would never tackle a project such as this. Likely costs are in the thousands.

If your stairs do not curve the Shaw carpet should layout fine. I don't know if you are going wall to wall. If you are using this as a runner on stairs as you stated, you will serge the edges and they will come in about 3" on each side from wall exposing the wood of the stairs on each side. There will be the serge lines on each side that will create a frame for runner. Serging is when the carpeting is cut and then the ground color thread is used to wrap the unfinished edges.

Hey Happy New Year! You could do a overlapp of the carpet runner on the luxary vinyl plank, because before they install the carpet it would have wood edges for the carpet nailed to be put in, thus overlapping would be a problem, and it would best to leave the LVT as is because you are technically creating a second sub-floor on top of the exisitng staircase wood. thanks Purewal Contractors Inc

If you paid for a 'retread' then you might only get new wood on the treads. If you paid for the spindles to be removed, the Red Oak removed and replaced with matching white oak, then you have a right to be upset. It all depends on the contract. Stairs are tricky. They are expensive, they are tiring, they are tricky and then are (once again) expensive. **If your original talk (ie. contract) spoke about staining, the GC (not a wood professional by any stretch of the imagination) would assume the two woods could be matched once stain went down (very common to work this way). If you then changed your mind and went with a natural finish, the Red Oak stringers became a liability that never were properly addressed after that (ie. paid for removal). Did your GC use a finishing Carpenter? If s/he did not, the GC was saving money. What used to be on the stair treads? Do you have photos of before (old coverings) and after (new wood with finish)?