Also, i plan on having my parents mail things to me along the way, including valuables like money or whatever else. How exactly would I go about it. Would I simply have to know where I will be in, say, a week, tell them the city and have them mail it to the post office? How does that work to have them mail things to me along the way?
I would not have things mailed to you. Trying to figure out where to have things mailed and then hooking up with them is a major hassle. You will either get to the town too early and have to wait, or you will get there too late and the mail has been returned to a regional office, or the post office is closed, or you are at the wrong post office. I had to have some special order tires mailed to me, and I will never do that again. You do not want to have any appointments when living on the road; you want to be able to live life foot loose and fancy free, and go where the wind blows you. Mechanicals, side trips, detours, and hooking up with other riders are all possibilities that you don't want to have to forego because you have to be at a certain town at a certain time.
There's an art to getting things mailed to you, but I doubt it justifies a blanket ban.
Here's how you work the art: you figure out how fast you're moving, and guess how long it will take the post office to deliver mail. (Most places in the U.S., that's 3-7 days for first class.) Pick a small town on your route that's the appropriate number of days ahead of you, and call your trusted mailing agent (parent, spouse, child, friend), and ask them to mail your package. Preferably the next day, because you'll be a moving target! Make sure the guesstimmated delivery date is Monday through Friday, and you think you'll arrive during working hours -- call it 9 to 2, just in case. You want a town that has only one post office, and one that's big enough there's likely to be someone there all through the day.
Your mailing agent will address it:
Smalltown, State zip
and mark it, "Please hold for TransAm bicyclist, est. arrival June 22."
If you're on one of the AC routes, their maps include zip codes for every post office. You can also look up in a post office directory, or on google maps.
If you miss it (you arrive early, or the P.O. is closed), give the postmaster written directions. In one case, I tore off the bottom of an errata sheet, addressed to Postmaster, and on the inside of the fold wrote, "Please forward my mail to Nexttown, MT" and signed my name. It made it with no problems. Again, you'll need to guesstimate delivery times and mileage -- keep your maps handy!
I only completely missed one package. A couple were right on time, missed one that caught up a couple days later, and one was forwarded twice before I got it. Small town postmasters were almost always helpful and accomodating (except in Lolo, MT!).