Honestly, I've tried several seasoning mixes, but never really noticed much of a flavor difference no matter what I used. The real point of brining is to increase moisture not flavor anyways.
The ratios above sound about right...but use kosher salt..it you use table salt. cut it in half.
I wouldn't brine chicken more than about 6 hours or it may get a little salty.
Heat up the water just enough to get the salt and sugar to completely disolve, then cool it back down before adding the chicken. One way to speed up the process is to half the amount of water, then add ice to make up the difference and cool it back down.