Lets say because of injury or starting late, how many weigh-ins does a wrestler have to have to wrestle in a regional tourney? Or does it matter?

Minimum of 4 weigh In's

If there is an injury the wrestler could still weigh in and not wrestle.  This will still count as a weigh in.

Also, doesn't a wrestler have to have 4 weigh-ins at the weight they wrestle at? Like, you could be 89 all season but you would have to have 4 weigh-ins at 71 to wrestle 71 at regional. Right?

I'm pretty sure that with the new weight management plan all you have to have is 4 weighins at any weight to wrestle at regionals.  You do have to make the weight you plan to wrestle at regions by the saturday of state duals.  Keep in mind that after Christmas Day the two pound growth allowance counts as making the weight.  So in others words if an athlete wrestlers 135 up until the saturday of state duals they could go down to 132 (+2 after growth allowance) on that day (1/27) and wrestle 132 at regionals.  The athletes weight loss plan would also have to allow them to lose the extra 3 pounds (Athletes can only loss 1.5% of their body weight per week).  This is the way I understand it anyways. 

I will have to look into it, but I though before you could wrestle  you had to make base weight once. Without the growth allowance given. 

It has totally changed. E/R king is correct. Also the 50% rule is no longer in effect.

Also, It is a 4 mathces and/or a werstler could have weigh-in and three amtches at that weigh-ion and still have enough. I am on the advisory committee and we put this in place so that people that get hurt or come out late can still participate.