Is there going to be a long line for taxis at 1 am outside Beijing Capital Airport PEK!? Thanks

No, generally speaking, you won't wait for a long time. There are many taxis at that time. :)

Hi there, how much is the taxi fare from PEK to Dongsi metro station and is there a bus that travels from PEK to Dongsi - after 12am - 1am

Upon landing, you can take airport shuttle bus Xidan Night Line and arrive at Dongsishitiao Bridge first.
The ticket fare is CNY30 per person. The operating hours are from 00:00 to the last domestic flight arrival. After arriving, take a taxi to Dongsi Station.
If take the taxi from PEK to Dongsi Station, the cab fare is CNY100 to 110 at night.