Me and my cousin are planning on going to the silk road, our time is limited for only 2 weeks

we'll be going there on the beginning of September, so we don't have much time to plan and prepare.
We are thinking of going to silk road. I got some questions here:

should we start from Xian? as that's what I saw what most travelers do.

is it too late to rent cars now?

would you recommend to travel by rent cars or by bus/train?

are the distances between scenery really far?

is it better to have a "base" somewhere, so you return there to rest after each day? or do you switch different hotels everyday?

we only have 2 weeks there, what are the recommendations on where to go in such short time? I know the place is huge...

Sorry about all these questions, it's my first time backpacking.

thank you.