The different layouts you see are probably 65%. 75% is 84 keys and has nearly all the same keys as a TKL but wrapped up tight. If it's missing FN keys, that is a 65% and if it is also missing the arrow keys, it's a 60%. There is also a 68 which is a TKL without FN keys and missing Home/End.
Also, 75% really is quite an uncommon size so options are extremely limited, if you want to piece it together from parts, your only real choice is Gonz (who seems to be extremely back ordered) or the EEPW84/XD84 out of China (Ali Express). While Gonz work is supposed to be good, my advice would be to pick neither, Gonz, as mentioned is backed up, and after my last experience with Ali Express, no thank you. It took 4 months to get all of the parts and I have yet to see if all of those worked. If something goes wrong, you may be waiting a long time and/or desoldering and re-soldering nearly 400 joints. Which is where I currently stand.
Which means buying a custom kit from a reputable source or a complete, the former is almost always sold out, the only good custom kit I'm aware of right now from a reputable seller is the
KBDfans75. If you want something better, you would be better to save your money and wait, but you may be waiting a long time and if it's better than the KBDfans75, expect 2-3 times the price. Customs get EXPENSIVE. Don't be surprised if you break $300 by the time you are done as even that is relatively cheap compared to many.
Completes fall into two categories, the typical layout or Vortex Race style.
The Race has a FN key above the backspace, while others put it near the space bar, why does it mater? If you accidentally hit the fn key while hitting the space bar (which happened to me a lot), it opens the calculator, stealing focus from whatever you are typing. Drove me insane, eventually I put a low profile keycap on it to prevent this. Unfortunately, The Race is pretty much the top 75% keyboard with everything else being of lesser quality and using a plastic chassis. Like I said, choices are limited.
Most of the common completes (some of which are quite good) can be found on mechanicalkeyboards.com or Amazon.
One last note, if you have a Mac, Noppoo and Drevo will not work.
Typical layout, Noppoo Choc Mini (note FN near spacebar):
https://deskthority.net/w/images/thumb/4/44/Noppoo_Choc_Mini_Top.jpg/800px-Noppoo_Choc_Mini_Top.jpgVortex Race layout (note FN above backspace):
https://mechanicalkeyboards.com/shop/images/products/large_120_RACE.jpg