Vortec engine questions-mounts, harness, computer

[almcbri]

Ok here are my rookie questions reguarding my new engine. It is a 5.3 Vortec.

Will I have to buy an aftermarket motor mounts? If so what are my options out there?

I understand I will have to send my wiring harness and computer off to get reflashed? What companies do this and who would you recommend?
I do not have a wiring harness or computer yet, so if there are companies that sell a harness that is available for my set-up, please let me know!

I hear there are some companies that make an adapter bracket to use a TH400 with a newer LS1/ vortec style engine. I can't figure out who sells these?

Thanks,
Andrew