Shadow priests don't work with a rotation, they work with a priority system. Priority is always keeping all dots up, recasting where needed, and using filler spills like Mind Flay and Mind blast to fill the gaps. Mind spike is not supposed to be in the priority system, it's designed for trash / quick removal of dots, and keep shadowfiend on cd.
Might I add that
www.shadowpriest.com is a very useful source of information.
EDIT: in regards to procs, it's only shadow orbs that 'proc'. They've recently changed its mechanic, I'm not a 100 % sure but I think you cast mind blast at 3 shadow orbs and then your periodic damage will do 20 % more damage for a set amount of time. I think. Take a grain of salt with this one.