I'm a long distance road biker, I'd say upgrading the saddle and getting some reasonably comfy padded tights is well worth the money. You don't have to be in spandex.

Saddle currently: Selle TRK (pick a width based on how wide your sitz bones are) Bibs: you gotta decide here. I might recommend Patagonia's MTB stuff if you want something fairly multipurpose that works with camping (if you've got the money)

Gravel tyres with good rolling resistance on road, paniers and rack, tough phone mount, consider raised handle bars and aero bars for long distance comfort. Two water bottles is good if you don't want a bladder in a pack. Go as light as possible. Tent, sleeping bag, mattress, etc. all super super light and compact hiker stuff.

Have you seen these giant helium balloons for hiking? They're maybe four feet in diameter, tie the balloon to your bike or pack, tie the bike or back to your wrist. Let the balloon carry the weight, and you just tow it along.

I don't know. I'm sure this will be no use to you. I just think it's cool, I saw yesterday, and I wanted to talk about it.

It depends on how you want to ride. Some just take credit card, stay in hotels and buy stuff as they need it.

As for the bikepacking you probably mean you need 2 things.

1. add rack or other mounting for your bags.

2. make it as comfortable as possible. Grips, saddle, pedals and adjust it to your liking. You may add some "horns" for more hand positions and stuff like that.

I would say that for shorter trips you just don't need anything special. I helped my friends to go on bikepacking trip and one of them resorted to using backpack tied to rear rack by inner tube.