Help me understand computer options

My swap is a drop-out 6.1l with TR6060. It came with a full wiring harness, PCM and gas pedal.

What are the options? Is there anything I can do with the harness and/or PCM that came with my drop-out or should that go on e-bay for some burnt out LX to use?

What's the main difference between Hotwire, Holley, FAST, etc? Are some more able to be tuned than others? Are some easier to get a basic tune going?