I think I was the main person that brought up LLC's on the other thread, so I guess I can chime in and give more details on my scenario.
I've been building pedals for several years and started selling them fairly early, and when I started keeping track of expenses versus income I was generally coming out a little ahead, I think I averaged $500-1000 profit or so per year after deducting parts. Most of it was cash as I primarily dealt locally, so as a starving college student with very little income anyway I don't think I even declared it.
About a year and a half ago I got a lucky break and found a niche, and I started selling 20 pedals a month, eventually increasing to 40 pedals a month. My income from pedals is almost as much as my income from my day job. My sister-in-law is an accountant and she walked me through the process of setting up an LLC. Depending on what state you live in (I'm in Illinois) it is usually affordable and easy to set up and run, I think I paid about $200 to set up the LLC and I just paid my renewal fee of $140 for the year a couple weeks ago.
Components used in building pedals that are being sold are a clear write-off, that is a direct business expense. Tools purchased directly for the purpose of building are also a clear business expense. Last year I bought a bigger CNC machine so I could mill more enclosures at once. Business expense. I also bought a UV printer so I can print my own enclosures. Business expense. I got new workbenches and shelves so I had room to build and organize everything. Business expenses. This year I got a new powdercoating setup to replace my cheaper old one. Business expense.
There are other things that she had me deduct last year that were gray areas, like recording equipment, guitars, and amps. I use them when I record demos to improve the quality of my demos, but obviously they are used outside of that purpose as well, so consult an accountant on that one.
As mentioned above, for the vast majority of people selling pedals as a hobby there isn't enough money moving to justify setting up a separate entity for taxes. I've given you my story, and if you're still thinking it might be worth it sit down with an accountant to get their professional opinion. If you don't know an accountant personally it would absolutely be worth it to pay for a consultation, and obviously you can write that fee off as a business expense
I hope this helps, and I'd be happy to answer any other questions.