1. Can you let me know what the most up to date stable version of Asterisk is?
asterisk 13 is latest and stable version , you check the below link for other stable versions of asterisk
2. Is there a pre-built package that would provide a billing and call logging software solution?
you can Elastix ISO which has inbuilt asterisk , freepbx, a2billing
3. Is Call Recording a simple solution (i.e.; is it as simple as implementing a module?)
very simple , if you use elastix, freepbx then its just a click to enable recording
4. Are there any limitations to what the system can do when compared to an alternative solution?
there are lot of features , its opensource no limitations
check the below link of the asterisk feature list