On a separate note, what are day-to-day expenses like if I camp along the route, and to what extent do I need to plan accommodation / camp sites in advance?
I hesitate to say on expenses because they can vary so widely depending on your choices.
I will say that we averaged less than $5 per person per day for mostly campsites, one night in a motel, one in a yurt, and one night in a tee-pee. That was with three of us sharing a tent, but you could do as well solo if careful. We probably stayed for free more than half the time. We camped in town parks a lot, stayed with a few hosts, and slept in a few churches. Listings for a lot of that is on the TA maps, but we also improvised if asked. We never really stealth camped on that trip and just didn't find stealth necessary in order to find free places most of the time.
Food can vary widely between individuals. If eating in restaurants as frequently as we did and cooking some as well, I would say $10 per day is possible without going crazy frugal, $15 is comfortable, and $20 is generous. It helps if you mostly drink water with any meals. We did drink quite a few sport drinks at breaks and they were a significant portion of our budget.
All that said, folks have done it on $5 or less for food while others spend $50 or more.
If you drink alcohol frequently the numbers would go up a good bit.
EDIT: I forgot to mention reservations. I typically never plan ahead more than a day or two if even that and typically do not make any reservations even then. I don't think we ever made a reservation on the TA. There are times when towns are spaced widely enough that you need to have an idea of where you will stop a couple days out, but most of the time that isn't even necessary.