I am intentionally ignorant of tubeless. Can't help.
I typically run about 67 to 75 percent as much pressure in my front tire as in my rear, as the rear is where most of the weight is. That has always worked well for me, both touring with a heavy load and unladen.
You said you found a wheel builder that can work with Rohloff hubs. I have no clue how old your hub is. Is it old enough that you lack the reinforcing rings?
https://www.rohloff.de/en/company/news/news/flange-support-ringsThe wheel builder will of course need the right length of spokes. Once you decide on rims, you should communicate with the builder in advance to make sure they have what they need for spokes and nipples. If your bike was built by Thorn, the rear hub is likely 32 spoke, but some Rohloffs are 36 spoke. (Mine is 36, I built up my wheels, bought the 36 spoke hub I wanted for heavy touring.)
Sapim Polyax nipples work better with generic hubs when fitted to a Rohloff. The nipples come in different lengths.
https://www.sapim.be/nipples/design/polyaxI assume you know the above (rings, spokes, nipples, etc.), but I mention it just in case you did not.
Good luck on your transition to tubeless.