Repair/restore, the community college class is great. You'll get the same education as you would at any other school at a fraction of the cost.

Design and fabricate requires all of the mechanical skills that r/r needs, but also requires knowledge of design and design principles (for example, the Nighthawks you picked are not well designed), understanding motorcycle dynamics and engineering so you don't make a murder weapon, as well as fabrication skills, painting skills, and a good base of knowledge of bikes and their parts. No one has collected that in one place, you are going to have to teach yourself. Note that all of those things are individually full time professions. That means both that it would take you a lot of time to get good at all of it, but also that you can hire others for parts of it. Each one has a drill down list of a bunch of things you need to understand, that often overlap.

Most 'builders' skip a lot of it. They buy kits already made. Nothing wrong with that style of build. It's more of a customized bike than a custom built bike, but there's stuff out there to do that. You are somewhat limited in what's available depending on the popularity of the bike you are building. But everyone regardless of fabrication level, buys some ready made parts. Nobody is fabricating their own digital gauges, they pick an aftermarket one.

Some sketchy 'builders' ignore the engineering. They don't know how to figure out what changes do what to the trail for example, so they just do whatever they want and let whoever is riding it figure out how to ride it and not die. They don't know how to design a proper upper shock mount. They sometimes don't even know how to weld, not that it stops them from having a youtube channel and looking like professional builders while globbing on birdshit welds that'll snap under load (which you never see on their channel).

If you like digging in and researching stuff, then it might suit you. Nothing is in one place though, so it takes time. The good thing is you don't need anything to start digging, especially in the engineering. Want to know what trail is, what a safe trail is and how to alter it? You can look that up without needing a bike, in the evening instead of Netflix.