D grade is the bottom grade at Calga, E grade is for kids/people over 75 y.o who can only do 25kms, everyone else starts in D. You will not get shelled in D

25 km per lap, so yes, 12.5kms out, 12.5 back again. Blood is 3kms from the finish. Best place to attack is for you to decide but yes, Blood is a good place to do it if you are a good climber. There are a few other rises on the course but nothing as steep as Blood Hill, just longer gradual climbs.