Seems like the main difference/difficulty is the extra steps required to see how people interact with it in context up on the wall. Hope you have a budget to design and print giant prototypes! :) I don't think "best practices" change as much as internal workflow. You still need to observe users in context & note what works vs what doesn't, but if the product is big then work BIG.
Some practical considerations:
It takes more time, computing power, and budget to work at wall-sized 4K than it does to design a website UI for laptop use. This = slower iterations, greater expense, and potentially greater impact on testing from hardware glitches.
People aren't as familiar with interaction patterns at that scale so they might not even have expectations yet, whereas they generally have an idea how a website or mobile app should work.
- For example, does "pinch to zoom" with thumb & finger still work, or do they need to scale up their gestures accordingly? Do they even consider gestures an option? This is still the same process of observation & discovery as you might normally test - just perhaps w/different assumptions.
How much latency is acceptable to people at that size vs. on a mobile phone? Does that scale too?
Are environmental factors more distracting at that size (lighting, glare, noise, having an audience, etc)? Does a low-fi mockup look even worse & therefore more distracting, meaning you need high-res mockups earlier in the process?
The Samsung "Centerstage" interactive kiosk is a great example, and this piece from Motionographer describes the design company's thought process and some considerations for design and user/audience interaction.
For example, novice users get up close & just tap, whereas store employees trained on its use have fun impressing people w/big sweeping gestures.
There's also the consideration of audiences. You have the primary "user" actually interacting, but it's also a huge showpiece that can attract a passive audience of onlookers. Those passive onlookers may learn by watching and change how they'd interact, so they're no longer "virgin" users.
One other thing I noticed from the "Behind the Scenes" video is that even in their internal meetings the team is often shown working at scale. They might do initial designs on a desktop monitor, but it seems that as much as possible they're looking at code up on a giant wall alongside the giant motion graphics & images.