So I guess that means my public/private address will also exist in the new Ethereum coin, and probably Trezor devices will have an option to use Eth Classic, Eth POW, and Eth POS.

But how would I tell my Trezor to use POS coin, under the existing POW address?

Also, what's stopping me from selling my POW coins and adding them to the duplicated coins in my POS address?

Sorry for the newbie questions, but from a purely ETH investing point of view, is there anything I need to worry about or do before/after the switch the POS?

I want to invest in the most updated version of Ethereum supported by Vitalik.

I already have some ETH. After POS, will there be a new Ethereum coin whereby I will have to move/trade my ETH-POW to ETH-POS?
Or will my existing ETH already be updated to run on the new POS system so I don't need to worry about anything?

I guess my concern is that I'm going to be stocking up on ETH, and I don't want to wake up one morning and find out I'm on some outdated coin and the train has left on some newer Ethereum coin and I've missed out...