Newbie need advice on size and set up

I will be moving out of my parents place in a month or so and can finallly look into getting some Axolotls. as my dad didn't see the point in them and my mom refused to have any pets in the house that didn't Meow or Bark.

I have been offerd a 100 gallon tank with the dementions 72 long, 18 wide, 18 high with mesh dividers and graval. I will not use the graval because i know that axies eat it.
Ive read bear bottom can freak them out. Do you guys prefer fine sand or slate tile for substate or is bare bottom the way to go?
Also confused about size ratio per axie some say 10 gallons and others 20. what are your opinions on how many i should keep in this tank?
I was wondering what filter to use?
How high to fill water for juvaniles?

I'm sure i could find some of this info in other threads i'm just not looking hard enough. so if any of this is repeated questions i apologize. i'm just so exited and nervous i have wanted axies since i saw them at a show about 10 years ago.

Don't worry- that's why we're here!
Awesome size tank- excellent size to start out with. As to set up, a few things to consider are:
Do you want plants? In which case a substrate of some sort is going to be needed for them. Avoid Tahitian Moon sand, as there has been a case of a larger piece of it killing an axie
In my own experiences with sand, it's been excellent, the axies have enjoyed it, cleaning with a siphon has worked well and grounding ornaments/play equipment is a lot easier.
In terms of slate there is the chance of gunk getting stuck underneath it unless you silicone it down, which simply means you'll need to have a method of lifting up the slate to clear it out.
As to a bare bottom, there are advantages in keeping it clean, but in terms of aesthetics a substrate can look much better.
Another topic which is quite popular at the moment is the walstad tank- search it in the forums/wiki for a bit more (this is the option I'm using on my new tank), though this is a more complex setup (Hopefully the long-term results will be worth it!)

As to how many in your tank, it depends... the floor space (going by the square foot rule) would give you enough for 9, as would the ten gallon rule for water (Which is the one most people go by). But by the same token, it may be better on you starting out to only have two or three whilst you get your head around the joy of axie ownership. This does, of course, mean you have extra space to expand if someone catches your heart

Also, welcome to the addiction!!

Thanks for the heads up about the moon sand as it was on sale at the fish store I visited last week. I almost bought it but didn’t when I was offered free slate from my brother and got confused again on what to use. He has already given them to me so I will make hides if I go with sand botton and at least some of the tile will get used. I think the slate stone hides will look more natural than the PVC pipe ones I was planning to get. If I go with the tile bottom I will definitely silicone them down as I can see your point how cleaning under could be an issue.

I haven't really given much thought to plants. I thought since the axies didn't like light I couldn’t have plants. I guess I will have to decide on plants or no plants before I make my decision about the floor.
Do live plants benefit the axies or are plants just decorative?

So many color morphs including gfp it will be hard to only pick 2 or 3 but I agree since I haven’t owned one before it might be a bit of a learning curve for me. I’m sure I will end up getting more because it may look a bit empty with 2 in such a large tank and who can resist those axie faces.

I can hardly wait to get the little cuties still have a few months before the old tenants move out and I can move into the apartment. Who knew that a pet you haven’t even purchased yet could be so addicting.