If I'm reading your plan correctly, you're gaining 7" of vertical height on the left side, through about 151" of track length, including a lot of curves. That's a 4.6% grade, almost as steep as the Lionel #110 Trestle set. With rubber-tired locos and speed control you can get away with murder. But personally I wouldn't be comfortable with anything steeper than 2.5%.
Since it's not advisable to build a yard on graded track, I would scrap the gold/yellow 3-track yard on the diagonal part of the platform, and start your grade one full track after the underpass. That will give you a much longer "run" to achieve the height increase, and a gentler grade.
To promote easy access, I would put the single gold siding in FRONT of the new, graded mainline, on the diagonal, instead of horizontally inside the "bowl" where it would be hard to reach for coupling, etc. My $.02.
