Yes, you can buy DMA hardware through AliExpress, there are legitimate sellers on there but also some scam sellers too that sell fake products (they won't be as good as the real thing). For example, a lot of fusers on there are knock-offs but they function quite similar to the real thing, then you have shit knock-offs that are just horrendous, its just a bit of a gamble if you want to buy off of there. In saying that, one of my friends has had no issues at all buying knock-offs while another friend bought a knock-off and it was complete rubbish.
CaptainDMA, Enigma, etc most likely source all of their hardware from the same vendors. They ALL come from the Chinese market and then are drop shipped to the western market. Personally, I've bought most of my hardware off of CaptainDMA and never had any issues with their products what-so-ever, I think the only other thing I bought was the Ferrum which I got from Ferrum themselves. You can also buy bundles off of other vendors like Spadegear which sell you the card, fuser and an aim device all in one but its basically the bare minimum in terms of quality for those packages (at least it was a few months ago, not sure what products they bundle together now).
The difference between 35,75 and 100T is just how much 'data' can be loaded onto the chip. Its essentially how big of a firmware you can load on the card, do keep in mind that just because the 100T is bigger and more expensive does not mean its currently better. Quite a lot of firmware vendors don't actually support the 100T yet - probably because its not required just yet for the modern anti-cheat market. Most people have moved onto the 75T and almost every firmware runs fine on the 75T.
Please recommend a Dma product.