Not sure how dark the taupe is but you’ll likely need 2 good coats for coverage needed.

Do you already have gray tones in your room - floors, sofa, fireplace, etc.? If not, replacing taupe with gray might not be the best choice.

I dont think you need to prime the walls. Most paints nowadays cover well with two coats. If you were painting your walls white definitely prime. Going from a taupe color you should be ok. If it is super dark yes prime.

i am only familar with repose gray not the other color. Repose Gray is super pretty lightened by 50%. Since your room is dark you could lighten it to see if you like it. I know this color works lightened. Some colors dont work at alll. Also, repose gray is beautiful full strength. You can always make a room brighter with lamps, mirrors, and select furnishings if you go full strength. I personally, like a little more saturation on the walls. it makes it feel more cozy.

A photo would help but for color I like SW Repose Gray depending on floor and cabinet colors. I doubt you would need to prime it but I always check with my painter.

If your walls have been previously painted and are in good shape (no peeling/flaking) and you are not doing much patching and your color change is not drastic, you can paint without priming.

I am curious why you are changing your neutral from taupe to a cooler gray. Not saying it is the wrong answer, but since gray is becoming less and less popular, it seems like an odd choice. Most people are moving from gray toward taupe.

Would you mind telling us the name/brand of your current wall color?

Would you mind sharing your reasoning?

If you don't have a lot of natural light, going from a taupe to gray doesn't seem like the best choice. If gray is a good choice because of your flooring and furnishing colors, try something light. Try cutting Repose Gray in half like the other commenter suggested. What is the color currently and what don't you like about it? Can you show us a picture of one of the rooms you'll be painting?