"But I'm not sure that 13 lit is enough space."
It depends on what you carry and how you carry it. When comparing pack volumes, take care insofar as I think sometimes you'll see just 'internal volume', whereas other times there's an assumption that you'll put things in outside pockets and external mesh, which can add a lot. I personally put a fair bit in external mesh, on longer or colder stretches at any rate.
"I'd like to know more about sending yourself stuff to the PO for personal pickup and SWMBO has been dehydrating things to try for backpacking. Might be better to go that route than to go to the store and pick things up. We wouldn't need money and resupplying would be quicker."
It's not difficult. Basically you send the package to a post office, and show I.D. when you go to pick it up. There are different mailing options, and some folks use a 'drift' aka 'bounce' box which depending on mailing options can be forwarded on to a next stop for free if unopened.
Most experienced long distance hikers I know (me included) prefer to minimize boxes sent to post offices and prefer to buy locally, except those with specific dietary restrictions. Smaller town post offices are closing and hours are more restricted, and it's not fun to get into a trail town on a Friday afternoon only to find that the p.o. holding your box doesn't open until Monday. And it can be challenging trying to put the right mix and quantity of food and whatever else in the resupply box.
"SWMBO has mentioned hostels a few times, but that just does't sound good to me. I don't care much for sleeping with a bunch of people I don't know. grin And I've seen the movie!!!"
Not sure what movie you have in mind, but hostels can vary quite a bit. Sometimes a place called a 'hostel' can offer inexpensive private rooms. Hostels are good also insofar as they usually "get" long distance hikers. You feel like you fit in better, and sometimes there are other advantages, such as options for rides from or back to the trail, or buying stove fuel by the ounce, or just hanging out perhaps with other hikers or other outdoor folks. Which sometimes in turn gets you info on trail conditions ahead, perhaps alerts to issues like fires burning on the trail, etc.
The other thing about hostels is that if you're tired enough, you'll sleep! :-)