To convert Dell workstation into gaming PC, this website has done a great job with collection of many Dell workstation, which is including T3600.  You can review their upgrade guide to find compatible components for your rig  https://www.greenpcgamers.com/dell/dell-precision-models/precision-ddr3-based-workstations/make-my-precision-t3600-in-to-a-gaming-computer/

1.  Yes, Xeon E5-2687W is compatible with Precision T3600.

2.  Same, Xeon E5-2687W is one of best CPU for this system, the other CPU is Xeon E5-1660.

3.  Can you upgrade BIOS to A19, NO, you can't if you must ask.