The simplest thing to do and most consistent is using as ONE SHOT. That is, use it and dump it. As to full strength or 1:1, it actually doesn't make that much difference unless you know exactly what you want and rest of your processes are consistent enough to guarantee uniform result.

One thing to be careful with when using D76 is the minimum amount of developer required. This is kind of buried in the documentation somewhere. For a roll of film, be it 35mm or 120, it requires 8 oz of D-76. That means for 35mm, full strength and 120, 1:1 is required. That's exactly what I do. You can extend the development time and use half of this but I'm kind of impatient so I choose not to.

One suggestion. Rather than using a one gallon container, use a bunch of smaller ones. Exposure to air (actually oxygen) reduces its life. So if you have a big jug and open it every time, AND have so much air in the jug as you use it more and more, it will degrade. Kodak says it lasts 6 months if full and 2 months if half full. The way I do it as follows:

1 gallon goes into one half gallon, one quarter gallon, and four 250cc (8 oz) bottles. Use the 8 oz ones first. When they are all empty, decant 1/4 gallon into them. When they are all empty, decant half gallon into smaller ones. Then quarter gallon gets poured into 8 oz bottles. This way, the bottles are always full and exposure to air is minimized. In my own darkroom, D-76 lasts at least 8 months. (I usually use them all up by then) It costs a little more initially but it's also convenient. One serving per bottle.