I think you pretty much covered it in your question. Granite has a grip, it is extremely hardwearing. it will stain however if you don't seal it. the stains tend to wash/bleach out over time though. my opinion is that it being a natural product the slight variations that will occur between each stone are exactly what makes it nice. Ceramic tiles may be the better option to provide the uniformity you require. there are more and more of these being brought to the market and they are extremely popular. the finishes vary and non slip ones are out there. the great asset is that they can be cleaned very easily. Couple that with the ease of grouting/pointing (you will be able to use a wet grouting mix and clean off as you go) it makes for a very practical solution. they will need to be laid on a concrete screed for best results which is an added cost.

Don’t do it! There is a reason why you can’t find examples on Pinterest and that’s because it’s not a great look. At a push you could edge all round with one colour and fill in with the other, but again I’m not sure. If you want to add some colour or interest some people use outdoor rugs. They are tough and can be left out in the rain.

I have porcelain and Indian Sandstone in my garden. Porcelain comes in different R ratings (R9 - R13). The higher the rater the better the non slip effect. Mine is R13 and is completely non slip even in the pouring rain. The drawback is the non slip finish means it holds onto dirt and can get grubby (mine does), so rather annoying! Never have the R13 indoors as cleaning it is difficult. The sandstone is a natural finish that comes in a riven rustic finish and a calibrated finish which is more modern and straight edged. It comes in many shades from grey, beige, pale green etc. I’m not suggesting what you choose but a paving that is difficult to clean is a right pain! Riven Sandstone in my garden Calibrated Sandstone My R13 Porcelain just after laying - looks a bit grubbier now!

I think grey too! Last month we had a small patio put around our shed too. I really struggled to find slabs that I liked. In the end we went with these - they are actually concrete (which I wanted because the patio sits level with my grass and I didn’t want lawn feed to stain). My landscaper said they were fab to lay, and they match my real stone main patio really well. https://www.castacrete.co.uk/Decorative-Concrete-Paving/Courtyard-Paving-Collection/Old-Grey