I did a couple 1 night overnights to a nearby youth hostel when I was a teenager.

But my first real tour was Oregon to Maine. Kind of jumped right in, I guess.

Mistakes:
1. No loaded test ride prior. Sounds really dumb, and it was. Had to repack everything and move panniers back and forth to quiet speed wobbles.
2. Going out too hard at the outset trying to hang with my faster ride buddies, resulting in an inflamed achilles tendon that almost ended the trip. Had to back off a bit.
3. Not stopping to explore things enough. But the other 2 guys werent really into that so much.

Overall was a great trip.
Re your trip, are you concerned about the amount of traffic on your route?