How are newly created neurons recruited into existing networks?
There is a huge body of literature on axon growth cone guidance which will give you some insights into how the biology works.  Unfortunately, incorporating it all into a model is probably going to make it unwieldy unless your express purpose is to model the physiology, which doesn't seem like the case.

Here are some references:


  Hong K, Nishiyama M. (2010). From guidance signals to movement: signaling molecules governing growth cone turning. Neuroscientist, 16(1),65-78. 


This is pertinent because it explicitly mentions adult neurogenesis, as much of the subject is devoted to the developing nervous system in models like the developing chicken.


  Kolodkin AL, Tessier-Lavigne M (2011).  Mechanisms and molecules of neuronal wiring: a primer.  Cold Spring Harb Perspect Biol, 3(6), 1-14 Free PDF


To call Marc Tessier-Lavigne a leader in the field of neuronal growth would be an understatement.  This article also covers some of the cues of synaptogenesis as well.


  Simpson HD, Mortimer D, Goodhill GJ (2009).Theoretical models of neural circuit development.  Curr Top Dev Biol, 87, 1-51.


Regrettably, I do not have access to this article, but it appears to be more along the lines of computationally realistic representations.  It does state that their models for synaptic strengthening are based on Hebbian Learning, so that's at least in line with what you presumed that you needed.

In searching for more computational models, ephrins and integrins are two of the cell surface agents that are heavily involved in the process, so any abstractions of those would make for a good model.