Before I go crazy on sketchup , I'd like to throw out a couple of simple lines just to get the "feel" of the terrain. I'd start with this one, the total length is 4668 meters, including the existing oval section, I choose to go CW and got some 775m main straight, good enough for top gear, following a couple of wide turns to spread out the field before the real first tight corner, I choose to include some tight corners, because...well, they're fun!
then some increasing radius corner, a fast corner that leads to a tricky stop, since the faster and wider you go, the worst you will do on the next one, so the right balance will give pilots various options, before the next hard stop, then direction change to a fast corner, a run for another medium tight corner followed by a DA that opens up (I love those) leading to a hairpin and an annoying section not unlike Catalunya's middle corner leading to yet another left that leads back to the oval. The pit lane can be located in the oval area. Hope you didn't get dizzy with my track, it's some 17 corners for 4.7K so it's not that bad because most corners are fast. I see 10 rights and 7 lefts so its fairly balanced for the tires.It's still at a very simple stage so it can be tweaked.