IMHO the lines on the shoulder are optional -i.e. whether to fix that or not is entirely up to you.
I've done both ways though I prefer leave them out and pretending they are panel lines... ^ ^
Also this one works well with the C-joint mod - i.e. you can separate the torso and waist as well as the shoulder frame from the torso and put 'em all together after painting. With c-joint mod it's even possible to paint using the spray can since almost no masking would be required...
For the back of shield, mask off the face and spray using dark grey or neutral grey followed with light wash~
people living in glass colonies shouldn't throw nuclear stones.