Yes an unlocked Achievement will only pop-up once, unless you Reset it.
If you Ctrl+F Search this post for “Resetting Stats” I wrote a few ways to reset stats and achievements.
Once you have Steam SDK / Steamworks integrated in your Project and make a Build it will automatically run Steam and play whatever build is uploaded (if any). So you have to upload it to Steam before it will work in Build (that is my experience at least).