Bitcoin-only firmware has been specifically designed to only cointain code enabling the Bitcoin wallet operations. No additional features or coins can be used while this firmware is loaded on a Trezor device.
No. You can switch to the bitcoin-only firmware without much of a hassle. Although recommended to have it ready, just in case, you will not need to use your recovery seed to upload the bitcoin-only firmware. If you ever find yourself needing to switch to the full-feature version, you can do it just as easily.
The private keys to your altcoins will remain safely stored within the Trezor environment. However, you won’t be able to manage or access your altcoins in Trezor Wallet until you reinstall the regular firmware.
Yes, the bitcoin-only firmware is available for both Trezor devices.