A lot of folks here rave about @Mickey's coffee rub on chicken.  In the interest of full disclosure I have to admit that I have never made it - but I have used a store-bought coffee rub on chicken that I like very much. 

Here is a description copied from Mickey's post from another thread:

Coffee Rub (turkey, chicken, beef & pork)

Equal part: Instant Expresso Ground coffee

Equal part: Brown Sugar

½ part: Black Pepper

½ part: Kosher Salt

½ part: Garlic Powder

¾ part: Ancho Chili Powder


Don't worry on exact, just close on measurement. I used to use turbinado sugar but we like with brown better. This is pulled from MollyShark, Hungry Man, & Richard In Fl then tweaked. I find the ancho chili powder is far less expensive in the bulk spice area than the bottled area ( have used both light or dark version). I make it starting with a half cup Instant Expresso Ground coffee and work from there as it seems to store well if sealed.

How large are your chickens? Too big and they will be tough. No more than four pounds. Brining or marinating definitely will make a huge difference. Look up Steve  Rachein's Bahamian Chicken on the web or this forum. You can use a whole spatched chicken instead of just the breast. Really really good. 

Yup, you gotta try the white BBQ sauce on chicken if you haven't already done it.  Just google Big Bob Gibson chicken with white BBQ sauce.  There are quite a few variations out there but they're all basically the same.  2 critical things to me.  First, make sure you're using a recipe that has cayenne in the BBQ sauce.  Gotta have that kick to fight against the vinegar.  Second, make sure you have some hickory chunks on your fire.  I've tried it with just charcoal and with other kinds of wood chunks and it isn't the same.  Have to have hickory.  Here's the recipe I use:

White BBQ Sauce
3/4	cup mayonnaise
2	tablespoons cider vinegar
2	teaspoons sugar
1/2	teaspoon prepared horseradish
1/2	teaspoon table salt
1/2	teaspoon ground black pepper
1/4	teaspoon cayenne pepper
Chicken
1	teaspoon table salt
1	teaspoon ground black pepper
1/2	teaspoon cayenne pepper
2	whole chickens (3 1/2- to 4-pound), patted dry and split (see photos)
	charcoal and hickory wood chunks
	Vegetable oil for grill grate

Instructions

1. For the sauce: Mix all ingredients in blender until smooth, about 1 minute.
   Refrigerate sauce in airtight container for at least 1 hour or up to 2 days.
   

2. For the chicken: Mix salt, black pepper, and cayenne in small bowl. Rub spice mixture all over chicken.
   

3. Setup grill for dual zone cooking and light grill, heat to 325ish.  Place chicken over indirect heat, skin side down on grill, and cover.

4. Grill chickens until skin is well browned, 35 to 45 minutes. Flip chickens skin side up and grill, covered, until breast meat registers 165 degrees on instant-read thermometer, 15 to 20 minutes longer.  You can move chicken over direct heat for a few minutes towards the end to crisp up the skin if you want.
   

5. Transfer chickens to cutting board, brush with 2 tablespoons sauce, tent with foil, and let rest 10 minutes. Remove foil and brush chicken with 1 tablespoon sauce. Carve and serve, passing remaining sauce at table.

And then I like to serve mine with slaw of some kind.  This is usually the one I use for this chicken recipe

Bookmarked

Try following Pepin's video https://www.youtube.com/watch?v=nfY0lrdXar8 and do a chicken ballotine. It's not as easy as Pepin makes it look, but it's also not as hard as you might imagine. I'd highly recommend deboning the chickens a few days ahead of time and dry brining them.

It gets easier to debone the chicken every time you do it, but the first one was difficult.

Chicken bombs are easy and great.

Evilsports said:

The chicken was a hit with the guests, but I was a bit underwhelmed.  I struggle with a crunchy skin in my BGE.  I cooked it direct at just under 400, and it was still too rubbery for my taste.  This included a few minutes of skin down to finish it.  Do you guys rest your birds under foil at all?  It's one of the last things that I suspect might be my issue..

I have to tell you, I've spatched several chickens and all have been a hit with the guests, but from my perspective the results always vary.  I get a lot of tips here and sometimes a technique works and other times it doesn't.  Some of my best chickens were fresh from the supermarket and directly to the grill, no rest.   Same technique yielded one of the worst.  Every bird seems to be different for me and I don't do half of the prep that you did.

I don't rest under foil though, and I've only flipped once to char the top-side (when it clearly wasn't the brown I wanted).

Guests loved it?  For the win! 

I have struggle finding the 3-4lbs. chickens recommended.  I usually end up with a 5lbs bird.  The next smaller ones are the cornish hens, but those are too small (I think?)

Glad you had fun though.  Had to be.  All that prep and experimentation.