So if I have my WTC on a MEW address via a Trezor this will be incorporated into the snapshot and I will be eligible for a GMN right?
Yes. It's not a MEW address, it's an Ethereum address. MEW just lets you send/receive on that address.
Once the main net is live they will port over the coins to the new chain using the same address but I would have to extract the private key from the seed if I wanted to move/claim any of those coins or wait until they announce integration with the hw wallet
They haven't announced how the migration to the new blockchain will work yet. Using a hardware wallet should not be an issue.
I guess as an addition, would the MEW address still show 5000 WTC or would I only see those coins via the WaltonChain address?
We will need to wait for confirmation on how they plan to migrate to their own blockchain first.
Effectively you just need to have your coins in your own ethereum address i.e. in your hardware wallet or on a paper wallet like MEW.