You bought 10 sewing machines in a month? Wow. Are you setting up a shop, or do you just like collecting machines? Either way, that's pretty cool. I have a few myself, lol.
Industrial machines aren't that specific, at least in the "gear" category. A medium-weight single-needle walking foot can do pretty much everything on a given store-bought backpack, except maybe proper bartacks and embroidery. Add some feet for zippers or cording, and maybe a binding attachment, and you're pretty much pro if you want to be. Beyond that, other machines or features are for efficiency, not capability.
About vintage machines: I completely agree, a good-condition Singer 201 or similar is a great find. But most vintage machines in antique malls, yard sales, etc. are not in good condition. They're rusty, the wiring is shot if it's an electric, they're missing pieces or the belts are shot, the stand is rotting if it's in a stand... or it's just overpriced because someone found one listed on eBay for $300 and thinks it's worth that much. Or, my favorite, they turn the stand into an Etsy project and sell the head separately (I bought this for $15 at an antique mall out of pity... The seller turned the table into an ugly "bar cart" for $150, and the head was just sitting in a corner.)
If you're interested, my collection is a 1930's National VB-TT that I restored myself, a Singer Child's Model 20, and a Juki 1508. Plus a Singer 14U46 serger, and a cheap plastic Brother, and that blue vintage machine head, if that counts. So... six? You're way ahead of me! (But I have a lot of machines at work to play with too.)
