I am very new at this.... how many cookies/brownies should I make for a 100 person wedding?

How many is the bride wanting?
Is there going to be cake served also?
Are the cookies/brownies favors?

Just so many questions just popped into my head. Maybe you can give us a bit more info. so that we can help you out.

depends on the size of the cookie and if there are going to be any other sweets there.......I would probably figure one of each for each guest if there's going to be a wedding cake....some people will probably have two cookies, some one, and some none.....with the cake you may end up with lots of waste......but I would err on the side of caution and make more than less.....but that depends on how much the bride/groom want to spend too.

I would recommend 2 per person at least if there is no other dessert.

What did they order? What are they willing to pay for?

It's actually for my boyfriend's sisters wedding that I am doing for free. She just asked me to make cookies/pastries. There will be no cake. I am making mini pecan tarts, mini cheesecakes and chocolate chips.