Extrude the front part towards the neck.
Insert a edge with Cut in bottom of the back and build the grid as shown.
Insert the edges vertically.
Lastly, select the 2 vertecies in red and weld them into one.
Build the polygon to connect the front part to the neck.
Insert with Cut the edges all around the neck.
Add a division with Cut.
One now will model decorations on the front of the armor.
For that select a face and with shif+Move make an Element copy.
Position there on the chest just away from the body.
Then extrude the edges to make a snake of faces, for the point at the end, use Collapse Edge.
Adjust in the user view the vertexes to have a harmonious curve as shown.
Insert a vertex with Divide into the edge, and continue to extrude the two curves.
The final result depends entirely on the care which you take to build this foundation, therefore try to spend some time here.
Insert into the model central edges with Cut, after having activated the 3DSnap in MidPoint mode.
Insert two new divisions here.
Lastly, insert a vertex with Divide and make visible the edges in red.