1. Can I also make a user defined seed of 24 words when I use Electrum together with Trezor?
2. Can I also make a wallet with some specific addresses/private keys when I use Electrum together with Trezor. (I mean a wallet with imported addresses/private keys.)
No, I don't believe that you can do either of these.
1. If you are using the Trezor with Electrum, you will be using the seed on the Trezor device so you wouldn't be able to specify a custom one.
2. You can only have a wallet using a seed or a wallet using imported addresses. You cannot have both at the same time. You will need to create separate wallets for this.
