If you cook, stainless has pros and cons. It is harder to keep looking good and you have to protect it from scratching. (think high maintenance, but looks great when new); cement, has pros and cons. Of course, weight is factor depending on your situation. If your kitchen is on a slab, weight not a problem, if not that is something to be considered. Some say concrete is hard to maintain and can have problems with the edges chipping. Granite is a cooks best friend. Granite is also competing with the marketing of Quartz, manmade products but for my dollar I would take granite any day. Simple "sealing" twice a year and no worries. Just a matter of personal choice. They all have pros and cons. Do you have some photos of your kitchen? What is styling? Need more information to help further.

I would not mix two materials, just go granite. If you want some "contrast" check out Jet Mist honed for your peripheral countertops. It looks like soapstone and would work nicely with most any other granite.

Can you versus should you?? You can cut on any of the solid surfaces list, but you shouldn't. Cutting boards save your knives, prevent cross contamination, ease transport of food, and save on clean up. Concrete and granite both need to be sealed and high acid foods break down the sealer, which if left overnight can etch or leave permanent marks. Stainless steel does scratch, dragging an item across it can leave scratches. You don't necessarily need hot pads on a solid surface though.

Can cement be any color ??? White? Cedar? Made to look like cedar boards???