I saw some news about lightning network recently, is this relevant to this project?
Yes it's, CommerceBlock sidechains are pegged to bitcoin network, so adding lightning network will be natural extension once the tech matures.
You mentioned there's no masternodes, but what is required other than a server to run a sidechain for payment in CBTs? Would it require a certain number of CBTs?
Yes, in order to run a sidechain participants need to hold and lock CBTs, the sidechains are PoS based. nodes running the sidechain will collect fees in CBT, in addition in the future will offer services that will run on top of sidechain to offer more advanced trade and commerce tools these services will collect CBTs as well.