Hard to say whether it's a bad idea. I think the best thing to do would be to take it slow and get to know each other better before jumping into anything. Being sober will well place you to evaluate him and see if he's a good partner a good person to have in your life. He's a bit of an unknown right now as you haven't seen each other in some years.
Personally I wouldn't be committing to anything more than lunch at this stage.