Short answer: Pedalboard comes with built-in (optional) input gain and output gain per pedal, so you should be able to bump the volume up enough to be comfortably audible going directly from guitar -> norns Pedalboard app -> headphones.
Longer answer(s):
Honestly even without Pedalboard, though, my guitar was decently audible just using the norns built-in âLevels > Headphone Gainâ parameter. But it certainly sounded much better once I added Overdrive (with +12dB input gain) and Reverb pedals to Pedalboard! Pedalboard doesnât have an âamp simulatorâ pedal, but Overdrive into Reverb does an okay job simulating an amp if thatâs what youâre after.
The bigger drawback is that Pedalboard is right now stereo by default â each effect is applied to each channel separately, so if you only have Left signal in, youâll only get Left signal out. The two exceptions to this are: Reverb (which reverberates the input signal in stereo space), and Delay in Ping-Pong mode (which will bouce your mono in back and forth between left and right outs). If you plug your instrument into the norns Left in, and then run from the norns Left out into your amp, then this all fine, but for headphones youâll probably get tired of only hearing in your left ear. Iâd recommend adding Reverb at the end of your chain with mix up pretty high, and then you can turn size and decay down to reduce the reverb amount (but keep the mono->stereo benefits). It shouldnât be too hard for me to add mono mode â I can do that before the v1.0.0 release 
Iâm sure one of the norns designers or someone with more technical knowledge could speak to this better than I could, but my understanding is that norns is ideally designed to be used with line level hardware (either consumer -10dBu or pro +4dBu), and basically every guitar outputs signal far below that. However, each pedal in the Pedalboard app offers an âinput gainâ control up to +12 dB, which may be very helpful if youâre plugging directly into norns and then out into your headphones. This would more or less mimic your âclean boostâ stage, but (just like whatever youâre using for clean boost) itâs going to boost noise as well as signal. A lot of clean boost pedals can have fancy techniques to reduce noise, but this is also kinda just the nature of the beast.