Yay, good for you for being brave & willing to learn something new! While it's still not my favorite job on the place (especially during the summer!) it has made me feel more empowered to have mastered this basic human survival skill.
You could process those birds at 16 weeks, or wait a few more weeks to let them grow a bit more. They won't get tougher, especially if you let them rest in the refrigerator a day or more, and cook them slowly with moisture. But they'll have a bit more meat on them. Some folks just don't want to keep pouring food into a bird that isn't going to efficiently turn it into flesh. It's up to you.
Your first session may be challenging, but you will certainly learn things to make future sessions much easier. It would be ideal if you could find someone with chicken processing experience, or even with hunting/cleaning game experience, to work alongside you. If not, even a brave friend or family member to provide moral support, good company, fetch tools, lend extra hands, scratch your nose for you, etc, would be helpful. Even if you have to go at it alone, remember that all of us here will be cyber-cheering you on & are there to answer questions.
There are a lot of helpful tutorials, and many that are not. Here's some of my favorites:
http://thedeliberateagrarian.blogspot.com/2006/08/processing-chickens-with-my-son.html This gives a good description of what to do though he makes you wish you had all those groovy gadgets he's invented & made.
http://thedeliberateagrarian.blogspot.com/2009/02/how-to-properly-scald-chicken-my-never.html This gives a great description of the scalding process, essential for easy & successful plucking.
This shows how to skin a chicken, if you wish to do that. Even if you don't it shows a GREAT way to easily clean out the carcasses.
You don't need much equipment to begin with, but most essential will be:
A good sharp knife if you're slitting the throat
Somewhere to hang the bird at about shoulder height by his tied-together legs for cutting/bleeding/plucking, like a tree branch or fence post or rafter
Something for a cone OR just duct-tape around his body, you just want to hold the wings still while it's finishing its last reflexive movements after it's Crossed The Road
A deep pot or bucket for scalding. Water can be heated on your stove inside, or on a grill or cookstove.
A table.flat surface at a comfortable height (about elbow high) for working
Hose with trigger sprayer close at hand
Good poultry shears for most of your cutting and/or a short sharp knife
A container for the blood, fleathers & innards
A cooler with ice water for the finished bird
Rubber gloves if you wish, I certainly use them!
Also, be sure to put the birds in a cage with no access to food, not even grass through the wires, for 12-18 hours before you process. They can & should have plenty of water, but no food. This will make it easier when you're cleaning them out.
Post any further questions & please let us know how it goes!
Enjoy your well-deserved meals!