First of all, thanks a lot, your info is very helpful.
I should have been more clear about the African countries. I wasn't so much worried about the time frame, but rather worried about getting my visa denied because I've travelled to these countries. I've seen various forum posts where people make it sound like visiting Arab or North African countries can mean a rejected visa.
If I try for the 90-day visa, should I just make all the bookings before even starting the visa process, so that I will be able to provide it when making the first contact with the Visa Center? And then they'll take a look and tell me whether I can start the application or not, based on whether they think I will get the visa? Just trying to understand the process more clearly. I am actually planning to eventually leave China to Kyrgyzstan from Xinjiang, but it seems that it's no problem once you have the visa.
In my country you apply at those Visa Service Centres, not at the consulate or embassy, I'm not sure if that makes any difference, btw.
I never thought about Mongolia as an option, so thanks for that. It seems that I will need a visa, maybe I should consider spending 7-10 days there. Is it possible to do anything worthwhile for 7-10 days in Mongolia on a budget? I'm already going to be spending a lot as I'm going to Central Asia afterwards, but I could probably cover the things I want to see in the South for 30 days and then Mongolia is neatly located for going to Shaanxi, Gansu and Xinjiang.