I can help with your VNAV problem too I think. Dial in a lower altitude in the altitude window of the autopilot. I usually turn it to the first crossing restriction. Then make sure you reduce the altitude before you're supposed to descend again.

Remember, just put in the new altitude. You shouldn't need to hit any buttons or anything like that.

Really, you could just dial it to the lowest altitude you want to go, regardless of restrictions. For example, say your lowest altitude is 2000ft, and you're currently at 36,000, but you have a crossing restriction at 12,000. If you put 2,000 in the altitude selector, it should still cross the restriction at 12,000 before starting its descent to 2,000. It'll do it all automatically.