You'll free-up about 20 hp with full roller rockers over stock stamped rockers as well as lowering oil temperature and it seems to me that there is more frictional area at the stud than there is at the valve tip, so it just makes sense to me to use full rollers.

12 degrees initial refers to ignition lead or advance.

It's up to you whether or not you want to degree the cam. If you don't intend to make any changes as far as advancing it or retarding it after you have the motor running, then I don't think it's that important. There are millions of motors in operation today that never had the cams degreed in. If you will advance or retard, I think it's important to degree the cam so you know exactly where the events are occuring so you can keep accurate records of the changes you make and their results. The other reason you may want to degree the cam is to assure yourself of the quality of the cam, in other words to make certain that each valve event occurs exactly where the grinder says it will occur.