They should start Jeremy Lin at PG and D'Angelo Russell at SG.
Russell is not a PG. He is a SG. He and Lin would work well together. Give them two dynamic ball-handlers who can run the PnR. Open up their offense.
A D.Russell + Lin backcourt > Russell + KCP
Russell needs help in the playmaking from his wings or bigs to work at PG. KCP does not provide that. Neither do other Nets players. Russell needs Lin.
If they get KCP, they should start KCP at SF.
As for how much KCP would improve the Nets = not much. 3-4 wins.