Chicken Breasts on Open Grill?

OK, basically on this, it's the amount of good burning coals that will determine temp. Real close together will be hotter than spread out. I would consider leaving a cooler section where things cooking too fast can chill for a bit. Also, just by estimating size from this pic, I'd want about 5 big Weber chimneys full of KB to start. I'd have some in reserve too, to add as you go. Moving stuff is another way you control temps. Wind will make this more problematic. If there is much wind, you're gonna NEED a windbreak.

Good luck!
Keep us posted.

Good info. from Phil . On an open grill ,I would do a bit of babysitting , so the heat doesn't jump up too high (for some reason ) .Other than that , you're covered ..

Have fun and good smoke your way ! ! !

Stan . . .

This is probably too much info. I don't know how much expeirence you have with larger groups. I actually do cater. Please don't be insulted if you already know all you need to know. :-) You did ask for some tips........
If you have access to a Camp Chef, or a heavy duty propane one burner, like from a turkey fryer or fish fryer, you can get a chimney of charcoal going in a hurry. Adding unlit coals over lit ones will help even out the temperature in the grill pan. I‘d keep a spray bottle of water handy to kill flare-ups, and slow things down when needed.
Get the potatos done first. They take the longest. Line the bottom of a cooler with cardboard or newspaper, throw the spuds in when they are done.
I do my corn in a big stockpot on the one burner stove. Bring the water to a full rolling boil, break the shucked ears in two, drop the corn in, and pull it out of the water after about 3 to 5 minutes. Throw it on the grill to dry it off a bit, get some light grill marks on it, and put it in the cooler on top of the potatos to keep it warm until ready to serve.
Take your time with the chicken, and keep the temperature moderate. I used have used a large home made charcoal grill a few times for large groups. (75 to 125 people ) Size wise, it looks a lot like what you have available. (but not as pretty ! ) :-) I like to marinate the chicken in Italian dressing, or do a vinegar / salt brine. Only do the brine on chicken with the skin on. It needs the fat to cook right, and stay moist.
I start cooking on the left 1/3 of the grill. When the chicken, burgers, steaks, dogs, etc are ready to turn, they get turned over and placed in the center 1/3 of the grill. Fresh, uncooked meat then goes on the now available left side. Move the done food from the center to the right side warm holding / serving area. Repeat as necessary, rolling your food from left to right. It's easy to manage a lot of food this way, and keep it coming.
Good luck on your adventure ! I hope this helps. Enjoy the experience.

I use my propane weed burner to light ours. I put an even layer of charcoal in the pit and torch. Doesn't take long to get going. FYI I go through more than 18 pounds. Two to three times that much. So be prepared and have your chimney handy to add coals if needed.

Having a cooler are is a must as different size breasts will be done earlier.

A easy way to cook corn for a large group is in a large clean cooler. Shuck your corn, place in cooler. Pour enough boiling water to cover corn. Put in several sticks of butter and close lid. Depending on amount of corn takes about 15 minutes and holds for a really long time. Melted butter floats on surface so coats corn as your remove.

large foil roasting pans make for an OK impromptu cover, if needed.

I like your grill