it's quite hard to tell how hard it is to learn CS & CEL, that's not really measurable,
and depends on a lot of factors, some of them depending on you
For tutorials, the manual is a good starting point (see CS/apps/tutorial/ too).
There's also a script (CS/scripts/jamtemplate/createproject.sh) which helps
a lot at quickstarting an app using CS (and possibly CEL).
Then, the API manual with its list of interfaces also is of great value,
even just to check what's available.