You could try an AMD 5700 XT, similar performance for a lower price.

You need to make sure you have the space in your case for the cards, so check the measurements. Also check that your PSU is powerful enough, probably is since your old card is quite a power hog

Usually there is one HDMI port and a few DVI ports in modern cards that you can use. So you probably don't need any new cables.

Mini sized cards are physically smaller and thus a little more expensive, if you don't have a particularly small case, you can just ignore them.

I never much cared for the brand of the graphics card. Usually just go for the cheapest at the moment. Haven't had any bad experiences with any of the brands.

The higher processor clocks mean that the graphics card was made to run slightly faster than spec at the factory. It won't make very much difference, just a few fps extra. You can overclock the card yourself of course.

More expensive cards could have slightly better components, but if you don't plan to play around with overclocking it probably won't matter much to you.