Calgary really has all the basics down by now (and it seems to be working great!), so I'm just popping in with some things that might make the cycling easier:
You want to replace the gravel with sand, which is a good idea. As you noticed gravel can easily lead to impactions (sand can do this as well, but it's less common than with gravel).
If you haven't replaced it yet, you could also consider putting the sand
on top of the gravel instead of replacing it. Like a thick layer of sand on top of it, so the axolotls can't reach the gravel anymore.
Even though your tank is uncycled, there are likely
some beneficial bacteria living in the gravel at the moment (they like rough surfaces). If you can keep those, it might give the cycle a little head start.
Pure ammonia is absolutely
fastest to cycle the tank (and it's easier to keep tabs on), but any source of ammonia will do. If you can get some pure ammonia, great, use it!
If you have to order it and this could take a few days, you can easily get the cycle started with other sources of ammonia, while you wait. Axolotl poop, rotting food, etc. - this is the stuff that will feed the cycle when it's done.
Cycling a tank indeed has a bit of a learning curve, but there are
tons of articles on it on the internet. Let us know if you'd like a basic summary/guide.
Honestly, I think 95% of axolotl issues can be prevented or solved with just good water quality and tank set-up. So that's good news! Once you've got it going you'll be set