I have a tar.gz backup of a wordpress site and I want to reinstate it under a new domain. I also want to rebrand the whole site with the new domain and brand name as well as redirect all forms to my new email address. What would need to be done?
Depending on what the zip contains, you can either just untar it on the server, and hope for the best, or you can do that on your own computer, separate out the things you need, install Wordpress properly on the server, and just upload the content to the database, and the theme/plugins needed. If the zip only contains the files for the Wordpress setup, it simply won't work, since it won't have the database backend to run off of. Personally, when moving Wordpress installations, I prefer to use a plugin for doing just that - it makes your life a lot simpler.
Thank you. The old domain expired, but I have a new one. I wouldn't mind buying back the old domain. I could reinstall it to the old domain and transfer it after. Would that be possible?
Depends - unless you could get back the old domain AND the database/installation, untouched, it won't make a difference. You could just untar it on your local machine, run a proper local webhost, install it there, and then copy it to the new domain/server. No need to get back the old domain, really.