1. If I store Bitcoin in Trezor and eventually I lost the device, can I retrieve the Bitcoion to any other wallets, including online wallets like Mycelium, using the master seeds.
Yes. Your seed phrase which you back up and recover all your coins stored on your Trezor. If you lost the Trezor, best to buy another Trezor, create new seed phrase and move transfer your coins one by one uisng the addresses generated by the new Trezor. Know that you have to do this because of the physical attack on Trezor which can make hackers that get in touch with the wallet to access your seed phrase. But while generating seed phrase, you can include passphrase which can help to generate different keys and addresses entirely. Anyone that will be able to generate the keys will need the passphrase along, which means you will have to protect the passphrase just like your seed phrase for backup.
2. Can I access my Bitcoin from elsewhere using my master seeds?
Seed phrase which is easier to import will be better, but also possible with the master private key.
3. Since it's more like a flash drive, I guess, what happens if it got corrupted by viruses? Or any malware?
Best to protect the device you use to access your hardware wallet, but know hardware wallets are resistant to malware. Only clipboard malware is possible, that is why it is good to check be recheck ymthe address you want to sent bitcoin to again and again before sending. If the address change to another, that is clipboard malware.