Soft luggage - the trade off is less security when you hop off the bike during the day. You could try looking around for someone you trust to watch them while you wander; other than that, just be accepting that theft happens. Some tank bags convert into backpacks.
Buy or ship - bikes are cheap in the US and shipping is another payment & hassle. Unless you can't find the bike you must have, buying stateside is wise.
Camping - at state-run campsites this can be surprisingly expensive (~$16/night). The Bureau of Land Management is a federal agency managing a lot of land, mostly in the west. You can camp on this land for free; find the land by using maps; highly recommended. Free camping is chancier (how do you feel about an angry farmers pointing a gun at you!) but if there is no owner around to ask for permission you'll probably be fine.
To help with getting a route together think about reading the excellent & quirky book titled 'Road Trip USA'
The US is perfect for a roadtrip - you'll love it - but consider including Canada, too.
Good luck!
JC
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James Courtier
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