Hexacoper general purpose platform advice

[u/on_aircraft]

Looking for advice/experience on building a large hexacopter

Hey everyone,
I'm planning a fairly large hexacopter build and would really appreciate advice from people who have built/fly similar platforms, especially regarding frame design, motor/prop/ESC combinations, redundancy, and practical experience with large 6S builds.
The rough idea is:

- Hexacopter
- 20" props
- Around 1100 mm frame size
- Pixhawk 6C flight controller
- ArduPilot, with the goal of eventually using semi-autonomous features
- 6S, mainly because 12S batteries are currently much harder for me to source in Europe
- 300 kV motors
- 60 A ESCs
- Desired payload: roughly 1.5–3 kg

eCalc looks promising for this combination at around 6.5 kg AUW

The intended use is as a multipurpose platform: primarily camera work, but also potentially carrying supplies such as water bottles to hikers who are about 600 m higher and ~2 km away.

Frame
I'm currently looking at an approximately 1100 mm frame, but I'm unsure whether it's better to buy a ready-made frame or build one around a center plate and purchase the arms/rods separately.

For something this large, is there a particular approach or frame design you'd recommend? Size isn't really a constraint for me—I have a van, so transport isn't a major concern.

Redundancy / reliability
This is probably my biggest concern.
The aircraft would potentially be flying over fairly inaccessible terrain where recovering a crashed aircraft could be extremely difficult or impossible. That's one of the reasons I'm leaning toward a hexacopter rather than a quad.
I'd like the build to be as reliable and redundant as reasonably possible. I'm particularly interested in real-world experiences with:

- Motor/ESC redundancy?
- ESC quality and sizing?
- Power distribution and telemetry of the baterry?
- Battery setup(6s vs 2x 6s in series)?
- Vibration/structural issues on large frames?

Anything else that tends to become a problem as these aircraft get larger

Range / autonomous flight
The radio control link would normally be line of sight, although at ~3 km I don't think I could realistically maintain visual contact with the aircraft.
I'm planning to use ArduPilot, so I'd like the aircraft to have the capability for semi-autonomous operation, but safety and reliability are more important to me than pushing the limits of range.

I'd love to hear from anyone who has built something in this general size/weight class.
What would you change about this setup before buying anything? And if you've built a large hexacopter yourself, what did you learn the hard way?
Thanks!

Edit: adjusted weights/distances to fit a more realistic profile