I don't worry exactly what the front/rear balance is, but do put more dense items in the front and/or low. Balance side to side, I kind of keep in mind but don't take great pains to balance. It isn't a big deal as long as you are in the ballpark.

I keep things grouped by when I need them. For example, I can pitch the tent and have my sleeping gear ready by opening one pannier. Clothes are all together except ones left out for quick access (those are usually under a pannier flap). I split clothes in zip-locks separated as clean, worn but can be worn again, and filthy must be washed before use.

I personally like panniers with only one big compartment rather than a lot of pockets. I then organize stuff within them using large zip-locks.

You preferences will probably be different and trial and error will find what works best for you.