Black stainless steel is simply regular stainless steel with a thin coating of paint. At some point, you inevitably will damage that coating. While stainless steel can be buffed out to remove scratches, this is impossible with coated steel. And even worse, rather than having a minor blemish in the grain, now you have a highly-visible difference in color.

I think you can definitely mix them. However, I wouldn't mix them on the same wall. For example, if your fridge and your range are on one wall in black stainless, you could add a regular stainless DW and microwave in the island. If you're going this route, carry the mixed metal idea through to your faucets, hardware, and lighting, too. Lots of great photos on this site with mixed metal finishes in kitchens. All that said, I wouldn't do this if you're planning to sell the house in a few years. If it's a look you love and you will be in your home for many years to come, go for it.

I too purchased the Tuscan kitchen suite and is thoroughly disgusted with Samsung's lack of accountability for their very expensive products. Since purchasing my suite in 2019 the dishwasher has been repaired twice in less that a year after purchasing (and a third time is in the makings), the frig has been repaired three times, and the stove is shedding its paint. This is totally unacceptable for 3 year old appliances. I searched everywhere trying to find Tuscan touch up paint to no avail; it doesn't exist. Samsung should honor these issues and replace my appliances. I honored their brand, they should honor their workmanship as well.

This is going to be beautiful! I'd go with stainless to lighting things up a bit. Also, I'm suspicious of the coating they use to make black stainless and I think the stainless will wear better.