Hi Mr. Richard,
For your first question, both of the two ways you mentioned to install capacitor bank is ok. It can be called local reactive power compensation. The capacitor bank can be installed in the main line or per motor/per distribution. The compensating capacity will be the difference.
For the second question, there is application and rebates for correcting the power factor and of course, there is saving for correcting the KVAR in the motor. I work for a company who is specializing in manufacturing reactive power compensation devices, APF(active power filter) and STATCOM to improve the power factor and efficiency. I am sorry that at present we do not have the formula information.
If you have any other queries, please contact me: liubaoyong2008@163.com
I will be happy to reply you .