How do you develop a social media calendar that boosts engagement?

Jao, it is quite difficult but not impossible. If you've a team, you can fairly do it. I would suggest you to explore blog posts of popular social media scheduling tool (those that are giants) as they frequently share ready to use content calendars.

It depends on your target, I would recommend to do some research and check when your target is mostly active - if you have active accounts on SM, just check the analitycs inside them. After that, fit that data up to your SM calendar.

This is not a straight answer. This depends on your target audience and their interest. But something that always works is memes on reels with relatable content! People love it