I recently had a reader ask me in what order my three big series should be read because he was recommending my work to a friend. I thought my answer would benefit you all, in case you were new to my stories yourself or also wanted to recommend my work.
I'd actually start with Book of David before OSL. It's shorter than OSL but introduces many similar themes. It's like practicing a short hike up a smaller hill before tackling Mt. Everest.
As for Billionaire, there's not as much overlap. I'd recommend reading it after CSL1. That way the reader sits on the happy ending of CSL1 for longer, can take a break by reading the Billionaire series, and after Billionaire come back to OSL and all the drama of CSL2. The exception would be to likewise take a break after A Billionaire's Life and save Tom Billionaire until after ASL1 because that comes later chronologically.
Happy reading!