This is when thinking about it and writing about it is FAR more complicated than the actual process. Go for it!
If I may suggest just one thing. If you are going to mix up ONE GALLON of D-76, may I suggest using lots of smaller bottles than one BIG bottle? Exposure to air is what kills the developer. If you fill, say 4 1 liter bottles and start using just one, then the rest will remain perfectly good for long time.