I brine all of my poultry, and generally inject a couple of ounces of the brine into the breasts as well. Recipes for brines are plentiful and although I've had wonderful success with salt to water ratios of 1 cup Mortons kosher:1 gallon, I prefer 3/4 cup Mortons kosher: 1 gallon, but also like weaker solutions as well.... I use white sugar (instead of brown sugar) when brining and injecting poultry. It dissolves nicely and eliminates any chances of staining the meat when injecting.
Even though I mentioned "cups" above..... My best brine tip is to get in the habit of weighing your salt, not using measuring tools. Salt varies from manufacturer to manufacturer in size and sometimes saltiness. So, a cup of Mortons is not the same as a cup of Diamond Crystal. And a cup of canning salt (my personal favorite for making brines) is way more salt than you get in a cup of kosher. Once you find out that you like a certain weight:water ratio, you will always be able to mix a brine with any kind of salt.
My best tip for split chickens is to split them at the pelvis, not on their axis. White meat and dark meat cook to different internal temperatures. White at 165*, dark is closer to 185*. It's really hard to cook traditional chicken halves because you have both kinds of meat on them. Here is they way I split and cook birds.
Butchering is easy, cut around each leg to the backbone, snap the pelvis (or use kitchen shears), then clean-up loose fat, etc.