Hey, Sorry to hear about your loss

T-Rex sounds like he was extremely well loved.
As for your tank, What size tank do you have? How long have you had everything sitting there? I would personally give everything a good rinse and go out and get new media for your filter.
You'll also want to grab some Water Conditioner to help remove any chlorine and chloramine in the tap water for when you do fill it up. You can also purchase a product that contains beneficial bacteria to help "kick-start" your tank cycling, but try and get something without aloe vera in it as this can add to your tanks bio-load quite significantly.
Another good idea kick-start the nitrogen cycle would be to add some live plants or some small fish just while you are getting everything set up. I'd recommend removing the smaller fish before you put your Axolotl in though.
Once your tank has been cycling for 7-10 days (Approximatley, depending on the size of your tank) It would be a good idea to purchase a test kit (Or even better, ask if your local pet store tests water as they often do this free of charge) as this will help determine the pH, Ammonia, Nitrate and Nitrite levels are perfect before you add your new Axie
Also, you didn't mention what type of filter you have, but seeing as you want a bare-bottom tank it might be a good idea to invest in some bio-noodles to use as a form of filter media. Good bacteria live in the substrate of tanks so by removing that you could have issues with establishing a good colony to help properly complete the nitrogen cycle. Bio-noodles sit in your filter and act as a "home" for the bacteria to live in and populate.
I think I've covered everything the best I can

Haha. Best of luck with setting up!