- As per my knowledge for every restart the sling ID gets changed : This is incorrect.Only if you clone the instance to another location, you need to regenerate the sling.id file. For a new instance, you don't need to do this.

Id prefer cloning the current primary instance along with datastore to a new location  and start as standby instance as if you start a fresh coldstandby instance, the time to sync over everything from primary would be very high.if cloning, copy everything along with datastore to a new location, find...

You can follow a similar approach as in (1) to do this on project level.(1) : Experiencing Adobe Experience Manager - Day CQ: AEM 6.3.1.0 - Show Custom Banners in Card, List, Column Views of Touch U…

Can you see if you get any exception in error.log or browser console once you try to install a package?Also, I think it might be that your java temp directory is full so clearing that or switching the temp directory to a different location should help here.

Satya,There is no developer version  of AEM. You can download AEM using Adobe licensing site or can request a trial from (1)(1) : AEM Download Request Form

Please add the error.log after installing package along with output of belowOutput of http://HOST:PORT/system/console/bundles.jsonOutput of http://HOST:PORT/crx/packmgr/service.jsp?cmd=ls

Search for  com.adobe.granite.workflow.content in Package manager and reinstall this package and see if they are available now

Can you use CRXDE to manually navigate to /etc/workflow/models and see if these models even exists ?

Please open a daycare ticket as this might require deeper investigation from Support team.

Can you stop the ACS commons bundle and retry