Good points! And also - whether there's a pattern in the carpet you choose. Patterns are an automatic markup for carpet installation due to the need to for pattern matching and making sure the carpet is cut perfectly straight (if the pattern is grid-like).
Binding is another thing you'll have to decide on, if going with carpet. It's something I hadn't thought of but needed to factor in the binding color into our decision. You should be able to get samples of binding colors, and even better if the carpet company is willing to sew a few inches of binding along the edge of your carpet sample to get an even better idea of what the finished product will look like.
"Carpet" sounds so unglamorous but there are really lots of LOVELY carpet options out there that work great as runners...we had lots to choose from. Here's what I looked at for some examples: https://andersontuftex.com/stairs (Anderson's curated list of options that are pet friendly for runners). We were very close to going with Madera in Indigo, it looked so cool. We ended up with another Anderson Tuftex option not on that list that our local carpet store pointed out to me.