Hi!
1. You are free to skip release as you wish, as long a you upgrade within a 18 month period (for Semi-Annual Channel releases that is). So, yes, you could upgrade from 1511 -> 1703 if you like. 1703 is now in SAC-B (former CBB) and with some luck we will get 1709 to SAC-B before end of support for 1511.
2. This depends a bit. You are of course able to defer them ONLY using the settings available in servicing plans. However, they are dependent of what you sync from WSUS, you could defer an upgrade there as well. Second, you are able to choose servicing channel and the days will be added to either when the version was released or declared SAC-B. But, remember that you still need to upgrade within 18 months from the initial release.
3. CB and CBB is the old terminology, its now called Semi-annual channel and SAC Broadly available, but they still work in the same way in many perspectives. One being that there are no technical difference between a SAC (SAC-T, T for targeted) and a SAC-B releases. SAC-B is just the released version + cumulative updates, but declared "business ready" by Microsoft. So yes, you can deploy it whenever you are ready.
I hope that answers your question - if you would like more information let me know.
