I was in this situation and it took 8years for me to receive any arrears or regularly CS. My ex didn't put in tax returns for 7years and when they caught up with him eventually they were done and this paid back most of the arreas (over $15000 by then) and I now receive CS monthly. I wouldn't expect to receive anything soon if your ex is the type to do everything possible to ensure you dont get anything. You will eventually get it but it may take a very very long time. I didn't receive any calls from CS just annual letters telling me what I should get. I had a call a few years later from them asking me if I would drop the CS as I hadn't received anything and I said no I wouldn't. So p-ssed of I would get a call like that when they didn't do anything to get it. I didn't know where ex worked and the one time they did start taking CS from his wage he quit and went elsewhere. I now don't receive any FTB for my eldest child but recieve the minimum for my younger 2 as they are children with my DH.
As far as I am aware CS arrears will remain until they are paid. Once the arrears get to big I am under the impression they can re-posses belongings to cover them or in the event of a death of the parent owing arreas it will also be paid through say super annuation/possessions etc.