Most of your questions seem to be answered by the current answers/comments, but since you are wanting more detail...
1) Did the plane, highlighted with a yellow circle, need to reverse to line up so neatly even though it just turned (I assume). Is the turning radius really that small that it takes very little space for a big plane to change direction so quickly on ground?
Yes, either the plane in the yellow circle or the one directly behind it had to be reversed into its spot. When airplanes are being repositioned around an airport, they are typically towed, because it requires less fuel and it's easier to start up a tug and hook it up than to power up a large jet for taxi. The tug is also able to push the jet backwards when needed.
Runway 11/29 at KPAE (currently closed except for taxiing for obvious reasons) has a width of 75ft (23m). According to Boeing, a 787-8 (the indicated plane and all but the green 747 at the northwest end) needs 128ft (38.9m) width to make a turn. This assumes a steering angle of 70 degrees, with the R2 outer gear at one edge at the beginning of the turn at a radius of 46ft and R3 nose gear at the opposite edge halfway through turn at a radius of 82ft. So it would not be possible for a 787 to turn around on that runway. Certainly not a 747. Even if they tried to do something like a three point turn, the distance between the nose and main gear is 74ft 9in center to center, which puts the wheel distance just over the runway width.
2) Is there any special reason that all the planes are on one side of the runway and not centered on the markers? They all seem to be lined up towards the left side of the picture.
They are probably on the south side to provide as much clearance as possible for taxiway D immediately to the north (as Lnafziger commented). The taxiway to the south is marked as closed (might be W?). The Additional Remarks on AirNav include (with my comments):
- ...TAXIWAY D BETWEEN D2 AND ALPHA (north section of D) RESTRICTED TO WINGSPAN OF 118' OR LESS. TAXIWAY D BETWEEN D2 AND GOLF (south section of D) RESTRICTED TO WINGSPAN OF 49' OR LESS.
- TAXIWAY W CLOSED INDEFINITELY (probably south of runway 11/29).
- TAXIWAY INTERSECTIONS D2, D3, AND D4 CLOSED INDEFINITELY (between runway 11/29 and taxiway D to the north).
For reference, the 787-8 has a wingspan of 197ft 3in (60.12m).
3) Isn't that too close when there is another plane parked so close in proximity? Provided there is ample space available.
While crew must certainly take care to avoid collisions, planes can be parked very closely together if needed. See your question 6 for an example (also boneyards or aircraft carrier hangars). Since the planes will also be towed out of their positions, jet blast should not be a concern.
Although there is more space at KPAE than on an aircraft carrier and fewer planes than at a boneyard, there were still issues of space with so many planes on the ground. There were issues with production and engine availability as slookabill mentioned, as well as the grounding due to the battery issues.
4) Is it just that the scale of this picture, taken from a satellite, making them look closer than they really are?
The picture seems to be taken from close to directly overhead, so the apparent distance is probably fairly representative.
5) What does that Double marking 7/91 Mean on the North East end of the small runway? usually that is a single number indicating the heading. That can't be 91, then what does that 91 mean?
As ratchetfreak mentioned, the marking is at the north end of the runway, so it is meant to be viewed facing south as 16L.
6) Why are there a bunch of planes that are about stacked on top of each other towards the bottom right of the photo, on the ramp to 29?
Similar to the reasons explained for the other questions, the planes are parked for some period of time. The ground crews want the planes to take up as little area as possible. These appear to be 737's and are probably parked either for maintenance or for reasons similar to the 787 (production).