Yes, you can have multiple Rokus and different models of Rokus on one Roku account. (I have read that there is a limit is 20 Rokus on the account at once.)
You can also delete/unlink older players from your account.
If you log into the Roku using the same account as the old one, it will automatically add in the same channels. On some services, even the service login may automatically apply. The order of the channels are unique to each device, so you will need to rearrange them if needed. Also, if a channel has it's own settings, (autoplay, privacy, etc...) you may need to adjust them on each device.