Looking at the first picture, that bridging solution would work, although if I was going that way, I'd probably increase the area of the plateau and tunnel the track, using a little back story for it's existence. That would just leave a bridge up onto the plateau that could pass over the circuit as it comes down off the plateau.
The gold could outline the larger plateau area, the yellow dots are slopped areas of track. And the solid yellow line would be a bridge up to plateau height. The plateau could run close to the track edge shortening the bridge.
For this type of track, whilst trying to keep it real,the tunnel is relatively straight and would be full throttle so it could be longer than what the real world would allow.
regarding the pitlanes,
My own personal preference is to have the pitlane on the inside of T1, though for a design such as this, an Abu Dhabi exit tunnel would be in keeping.
Where I placed my pitlane, the straight would be the same length as the old Silverstone pitlane the back of a long grid could ease around the final corner, much like at Woodcote. As for the garages, really your only looking at 250-275 metres including a race control building.