After adding, I published all pages to the new channel.
My problem now is that whenever I access the channel via ChannelService, the manually added channel’s Id is null. To be specific, here’s the screenshot.
That is per design. Kind of general pattern for most of the entities in Litium. What you set in BO when creating a channel is the name (Localizations) of the channel not the ID. You can set it in the DB tho. Or create it programmatically (through code).