Hello Sandman,

-You can think of the divide ratio as the closed loop gain from the input reference phase (input to phase/frequency detector) to the output phase (VCO output in most cases).  This effects the PLL in-band phase noise, to which the contributors are the PFD/CP, N divider, reference divider, basically everything except the VCO and loop filter resistor.  Therefore, a lower N value will give lower in-band phase noise.  The tradeoff of higher/lower reference frequency should also be evaluated when chosing the desired N value.
-The PLL loop filter components should be calculated for a given N value, along with Kd, Kvco, desired phase margin, and desired bandwidth. A larger N value will yield lower capacitor values and higher resistor values with all else being the same, which would increase the phase noise contribution from the resistor itself.
-Equations can be found in many basic PLL papers.  A good basic PLL document is PLL Performance, Simulation, and Design by Dean Banerjee, which I think can be downloaded for free from the National Semiconductor website.

Hope this helps.

Tim

Hello Tim and loose-electron,

Thanks for your inputs. I really appreciate it.

Cheers.