To answer your question first, I don't see Jordan Farmar supplanting Derek Fisher as Lakers' starting PG next season for several reasons:
Not a reliable outside shooter.
More foot speed than Fish, but lacks strength, defensive fundamentals.
Lacks D-Fish's grasp of the subtleties of the triangle.
The only problem with Derek Fisher is that he's no longer a starting caliber guard in this league.
I'd love to see Lakers acquire a veteran PG like New Orleans' Antonio Daniels, who might be available if Janero Pargo returns to the Hornets after a one-year stint in Europe.
As far as your Additional Details are concerned: With all due respect to your dad, it's too early to say with certainty that LA won't try to keep Shannon Brown. And I question the quality of the back up center you could get in any sign and trade deal involving Brown. Shannon Brown is a journeymen at this point in his career. An athletic, hard-nosed player, but a journeymen nevertheless.