How do injuries work in this game, meaning, at what point is it safe to play someone who still has an injury?

I usually pull someone from the lineup when their health is <50 in a specific area and put them back in when it hits 50. It's not an exact science though.

It also depends on the injury and what position the player plays. An OL with 30 in Leg is probably playable, but an RB with 30 in Leg, probably not.

Just out of curiosity, how does that work out?

This thread should help!

https://parody.myfootballnow.com/community/1/612?page=1

I am relatively new to MFN as well.

Is it normal to have 2 "doubtful" or "questionable" injuries of 5 to 9 weeks each happen every game to your starters?

This is what I have faced in the first 3 weeks of my season. And at this rate, I am not going to have any starters left by around week 9 or so.

Is this normal or am I doing something wrong to cause this?

Completely random. I've had seasons with few injuries. I have had seasons where I've had 7-8 major injuries.