New tank and new to puffers *need advice*

[Augustopuffer]

So I'm fairly new to the "aquarium game" and have a 10G that's been set up for about 6 months now. I have a friend that's had many tanks and currently has a 250g that's been coaching me but has never had a puffer so I've come here for advice . This is what I currently have:

10g Freshwater Tank
1 Fig 8 Puffer (1.5 inch)
2 Harlequin Ras
1 Brass Tetra
3 New born Platy
1 Ghost Shrimp

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I understand the tank is wayyy to small for the puffer so I've made the investment and bought a 75 gal tank which I'll move him in ASAP. I just bought 11 lbs of thin unique drift wood that fills about a 1/3 of the tank with many caves and obstacles. I bought 4 - 20lb bags of quarts sand (easy maintenance as it's heavier than normal sand) and will be being quite a few plants soon once driftwood is purged of most it's tannins. I'm buying a Fluval FX 5 in the next few weeks as well so ideally tank will be up in a month. Here are a few of my main questions before he goes in and I finish establishing the tank:

I would like to have MTS snails to clean the sand and prevent air pockets. Will they be ok with my puffer as I've heard they are hard and can possibly break teeth?
I've been feeding my puffer 1 pond snail the size of his eye a day which he quickly finds and eats. Is this a good amount or should I do more or less?
I've read so many mixed reviews about Fig 8 puffers and brackish water. Can he stay in freshwater forever or will I have to buy another tank in a while when he matures?
Any idea how big they are when they mature to adult hood and require brackish if need be?
I'm possibly thinking about 2 puffers in the 75gal with a hand full of small fish that are compatible. Is that ok?

[bertie 83]

Mts can break their teeth so it is a no go. F8 puffers are brackish fish sg 1.003-1.005 suits them best. 75 g would suit 2 but you would need to put the new one in first. Feed him until his tummy is slightly rounded 6x per week. Bumblebee gobies can make good tank mates and you could add quite a few in there. Welcome to the forum.

[Augustopuffer]

Thanks Bertie

Once the big tank established I will be converting the small 10 gal to a heavily planted tank. I'm wondering if a filtered/heated tank is better for breeding pond snails or a small tank with no heater or filter?

[Flutter]

Filtered and heated is better for breeding snails