Atlanta connection query

Just wondering if anyone on here had experience of getting a connecting flight at Atlanta on separate tickets? I'm arriving at 4.05pm on Virgin, then departing to Orlando at 7.25pm with Southwest. I will have a mobile boarding pass for Southwest (I'll check in online before I leave London) and just carry on luggage, so I'm wondering -

A) Do I need to leave the International Terminal, catch the shuttle to the Domestic Terminal, and then go through security there or can I clear security in the International Terminal and get the plane train to the concourse for my Orlando flight?

B) Will 3 hours be a comfortable connection time for a separate ticket connection?

Thanks

Hi
I done this route a couple of weeks ago. You go through security after you leave customs in the international terminal & than get on the train to the domestic terminals.
I only had a hour & a half for my connection & got through fine.