How many lines do you need to configure BGP?

Depends upon the requirement.

minimum need to have 2 commands and maximum up to the requirement.

Number of lines are depent upon the requirement , Minimum requirement is 2 commands

is depend of neighbor so the minimum are 2 command line  (it's mean one neighbor)

just one line to configure router as a bgp router

(config)#router bgp AS_NUBER

More than 5 lines of commands needed to configure BGP.

I THINK IT SHOULD BE MINIMUM 2 LINES AND ABOVE.

3 commands  for basic connection

router bgp 65001

bgp router-id 10.255.1.4

neighbour 10.254.0.44 remote-as 65007

Configuring BGP required 1 command, but making neighbourship required 1 more command to get established.

BGP is of two type one is EBGP and other in IBGP, best way of confuring BGP is if you have two ISP connection

more than two lines to be mainten in boarder gateway protocol.

There is only two command to configure BGP, But if any additional configuration required then its depend on.