LRS - Where to start?

Hi, we are currently getting some eLearning made for us by an external vendor that needs to be supported by an LRS. We would like to develop our own elearning in the future using this format (currently publishing in SCORM 2004) so it's important for us to gain some knowledge on what we can do with xAPI to make use of all functionality.

We are looking to use Cornerstones integrated LRS but the information from Cornerstone is very broad and doesn't say directly what exactly you need to do. If anyone has any experience of Cornerstones LRS, is it worth sticking to this or using an external provider we can link up? 

Is there anything that needs to be done within SL to use it's features other than changing the publishing format, it would be good to know if it would increase on build time.

My only real current understanding of xAPI format and any other new format we can publish in that exceeds this is that an LRS allows you to push information back in to an elearning package, which makes things like leaderboards possible. Past that my knowledge is super limited so I'd be really grateful if you could provide some guidance on the above.

Thank you :)