ᐅ Filling and smoothing chipboard in garden sheds

Hello,

I have upgraded my existing garden shed with insulation and a new corrugated metal roof! Inside, I covered the walls with OSB boards and the ceiling with particle boards. Unfortunately, the particle boards don’t have tongue and groove joints, and now I would like to apply fiberglass mesh tape on the joints and then paint the entire ceiling. What type of joint compound should I use (the shed is not heated in winter), and which paint would be best? Do I need to prime the particle boards first to prevent them from absorbing too much paint?

Best regards