Now if I understand this correctly, If I can use the same 24 word seeds on my new Model T, then there won't be a fee for moving my coins over from the old Model One to the new Model T?
You are correct that there will be no fee, but the reason there is no fee is because your coins don't move.
As we said above, your coins are not stored on your hardware wallet. Your coins are on the blockchain and never leave the blockchain. What your hardware wallet stores is the private keys which let you access these coins. Your seed phrase is used to generate these private keys. By importing your seed phrase to another hardware wallet, you are duplicating your private keys across both devices, so both devices can access your coins, which haven't moved.
If I can't safely figure that out, then my new Model T has a 12 word seed. If I just go with that, then there would be a fee for transferring from my old Model One to the new Model T?
In this case there would be a fee. By generating a new seed phrase you are generating a new set of private keys. If you want to transfer your coins from the addresses linked to your old private keys to an address linked with your new private keys, then you need to make a transaction to move the coins. Note that the coins only move from one location on the blockchain to a different location on the blockchain. Again, the only thing on your hardware wallets are the private keys allowing you to access those coins.