Switch gyro is a different animal to NEXUS - it's much smoother and easier to aim on NEXUS. I found BotW to be very clunky on Switch with gyro aim.
The interesting thing about using NEXUS is it's the way my 4 kids wanted to aim while learning to play video games. Every single one of them tilted the controller to aim and had to be taught to keep it still and use the sticks instead.
Motion Aim is very easy to adapt to, especially for ADS. It'll only take an hour or two to adjust, maybe less. I got it pretty much straight away and I've never been comfortable with gyro. Stick to the default NEXUS settings, aim mostly with the sticks and tilt the controller to get on-target.
I barely touch the right stick while ADS and aim almost entirely with Motion Aim. The only time I'll adjust the right stick is to swap targets or add more recoil control. This also frees up the right thumb for hitting A, B, X & Y, so I don't use the rear buttons at all for these bindings.
HIP takes more getting used to as Motion Aim is active all the time, but it just takes some tweaking and persistence to get right. I recently swapped from Motion Aim on ADS only to HIP as well and I'm doing just fine with it.
As for additional shoulder buttons, they're not necessary as the 4 buttons on the rear of the controller can be mapped to any controller action. Like you, I'll map the LS and RS buttons to rear buttons to reduce wear and tear, but haven't done it yet. I'll get onto that
Check my VODs on Twitch for a look at NEXUS in action. I have potato aim with a controller, but I aim well with a NEXUS. Like APEX, performance varies depending on the quality of the look mechanics, but when NEXUS works well, like in Destiny 2, it feels sublime. I'll get back to streaming next week if you want to watch a live demo and ask questions
