Hi All, I am totally new to Roots but very old WordPress user, it looks pretty interesting but how to start with Bedrock on localhost using GitLab and setup WordPress site, also it it important to use Sage Theme or this will work with any theme i work with? all the suggestions are appreciated.

You can use Bedrock with any theme. A Bedrock-based WordPress can be set up locally the same way you’d run WordPress normally. Just follow the docs.