If you are going to use large stones you have to ensure the stones are at least twice the size of the Axolotls head. 

I prefer using sand as its fairly easy to clean and looks the best in my opinion. 

If you prefer a bare bottom tank then yes for sure you can leave it bare. 

Sure, thank you!
Do you by any chance gave experience with using normal filter sand? Fine aquarium-grade silica is pretty much impossible for me to find. I have read that if you sterilise it properly it shouldn't be harmful? 

@saxolotl I have defiantly used myself and seen other use pool filter sand. As long as it is silica sand it should be ok.