You already can see that there are many different ways to resupply. But, sticking with your original questions, i’d say that if you are going to primarily ship your resupplies, ship them often. Unless the price of shipping is going to make your hike unaffordable, you’ll be grateful to be resupplying more and carrying less.
If you’re shipping from SF to the trail, beware the flat rate boxes. They will end up costing more.
Personally, i found resupplying from towns in California to be fun, reasonably cheap, and reasonably nutritious except for Kennedy Meadows and Bridgeport. For Oregon and Washington i mostly shipped to myself, and it was a boost to eat some better things more often. I liked the change partway through.
I bought and shipped ahead from Mt. Shasta City and Portland, instead of Ashland which is where everyone else shipped from. Ashland is spread out. Mt. Shasta has health food and supermarkets, PO and UPS, all within a couple of blocks. Ashland is more spread out. In Portland i had a girlfriend with a car.
If you’re concerned with nutrition, know that you can find health food of some sort in Idyllwild, from Agua Dulce if you find your way into the suburbs, in Mammoth Lakes, Truckee, Chester, Mt. Shasta, Ashland, Bend, Portland, and probably a few other places. Many healthy foods were in the hiker boxes in Warner Springs, Agua Dulce, Tuolumne Meadows, and Skykomish.
The things people tended to get sick of the most (judging from boxes) were power bars, and bulk dried starches like oatmeal, potatos, quinoa, etc.
markv