Our kids have been raiseing meat birds for 4-H fairs for 17 yr in Ca. 
Don't worry about the 25 chicks, a rule of thumb is that for every meat pen (3birds) you will need to raise 12 to pick from plus you have to figure in losses & maybe legs blowing
You need that many to choose from because they need to be like a colone on 1, the reason is that a market wants uniform birds all the same in the case, not fat ones mixed with skinny ones, uniforms makes a better looking case.
At 9 wks you'll have to worry ablut the birds going over weight if they are gd meat birds, so hold them with a moderate protein till about 3 1/2 wks before the fair, keep an eye on their weight you want them to weigh as near 5-51/4# as you can it is easier to put on weight than is to hold them back, if you have to hold them then you lose conditioning to feed them to grow slow then pour it on the end with a turkey/gamebird grow, something with a high protein, we use a "not less than" 24% protien.  Feed a supplement of bone meal, it helps from legs blowing out.  Change litter often, because of brest feathers & brest blister, & sores on the bottom of their feet, the problem is they don't roost.  You do best with picking birds of the same sex.  If you don't have 3 good uniform birds but you have 3 fair birds, then go with the fair. the reason is like I said 
they are judge on uniform so 3 fair with judge better than 2 gd 1 fair
I'm sure there might be people scratching their heads with what  I said but remeber this is for a competition.
let me know if I can help with anything 
Bill