Grades;
Grades are usually given individually and as an average that actually forms your final award grade, some first years do count but it tends to be weighted towards the end. All modules need to be passed to get a final award, or you may lose hons.
if you get 50% 50% and 80% and 80% in your four modules your average will be 65%
Postgraduate;
Can vary, most request a 2:1 but there are many that have gotten through, some people learn better later dependent on what's going on, the advice Id personally give anyone that's looking at a 2:2 is to make sure your dissertation is a 2:1 minimum if you wish to apply for postgrad. Unless its vastly oversubscribed they want you more to attend after all, they want the fees. Theres a balance between ability, a 51% and 51% dissertation. A 59% and 65% dissertation may tell someone different things.
Employers;
Depends, on the whole not really.
If you are going for a super elite department they have to separate people somehow.
Most professional registered roles care about the registration, little else.
Im not sure if that answered or not but maybe someone will be along with more specific