The Futian Station in Shenzhen is HUGE, and the walk from there to Civic Center would more likely take 10 minutes instead of 1. Also, it would take more than 4 minutes from Civic Center to Futian Checkpoint - I would say around 10 minutes. Line 4 is easily the busiest line in SZ metro system, so I personally would avoid that line during evening peak hours (northbound trains) and morning peak hours (southbound trains) on weekdays.

The "Business Bus" seems to be a poor translation from Chinese - I think it refers to a minivan, and you can clear both Mainland China and HK immigration on the car.