I agree with everything you posted if speaking about a single spey or switch cast. However, with the double spey, I've found that you can't use the "pre-load" forward movement before the D Loop is finished being formed with the long-belly line or the anchor will be pulled and the cast will collapse.
Also, since I've been using an underhand push along with a top hand pull to help power the D Loop in a single spey, I've found that I have to wait to apply this underhand push and top hand pull until after the line is aerialized from pulling the line up with the beginning of the rod sweep. I also find that making the rod sweep by rotating the body from the waist and not using my arms/shoulders to do so makes for a very energized line release from the water.
I have also found that the length of the rod figures into where the anchor is placed in relation to you. I've found with rods of 16' and longer, the anchor ought to be less than the rod's length away from you. This is very evident with 17' and 18' rods. When I place the anchor a rod's length away with the 17' and 18' rods, it is too far from the body to produce a good cast by virtue of the amount of curve introduced from having it placed so far from the body. Instead, I've found that with the 16' and longer rods, there is so much space available for the line, that placing the anchor about 13'-14' from the body works best. Notice that this is about the same place the anchor gets placed with rod of 15' or shorter.