Great work. You have great production value for your first YouTube video. Sound, editing, camera, slow-mo. It looks and sounds great. I also think you have a very ambitious and interesting project. I definitely want to see more.
I do have some constructive criticism - but keep in mind that I've never made a successful YouTube channel so I may not know what I'm talking about. I feel there is a difference between the promise of the video (nerf dart missile system) and the payoff of the video (electronic firing mechanism for pellet gun). That mismatch leaves me unsatisfied as a viewer.
For context, when I started watching your video I immediately started scanning with the video scrubber to look for instances of nerf rounds being shot out of the air. I was disappointed not to find any. Conversely, if the video was titled "Shooting pellets from my laptop" or something like that then I would not have been disappointed.
I would suggest structuring each video to follow each specific part of your project. Every time you have a deliverable, give a presentation of that deliverable, the specific part. When you have all the parts, then it will be time for the grand "putting it all together" video where you're shooting nerf rounds out of the sky.
With this approach to video making the first video would be entirely focused on the electronic firing mechanism for the gun. Show the gun, shoot the gun manually, discuss the vertical grouping, disassemble the gun, connect your electronics, and then the "payoff" or climax of the video is you shooting the gun from your laptop. Anything that distracts from the plot, that is, taking the audience from pellet gun to electronically fired pellet gun, should be cut from the video, unless you absolutely need it for future context (e.g. measuring the vertical grouping).
I would think about the video as like writing. Points that distract from the central message should be pruned. One example - your aside on microcontrollers. I think it's a fair bet that the kind of person who would watch this video already has a good idea what a microcontroller is, but even if they didn't, they would be very likely to infer that it is essentially a small computer from context.
I see you start the digression on microcontrollers at 10:37 and complete it at 11:00 - that's 23 seconds where you are essentially going away from the central idea of the video. This is just one digression. How much time could you cut from the video if you eliminated all digressions and made a tight focused video specifically on the deliverable?
A video that is concise and concentrated on message and delivers what it promises to the audience will, in my estimation, retain and please viewers. High audience retention will help you with the YouTube algorithm getting your video recommended to others.
Final suggestion - start with what you've built. i.e. Start by shooting the gun from the laptop, just a couple shots, to show the viewer you are going to deliver what your video promises, then walk through the process to finish up where you started - with the complete demo of the computer controlled firing process.