I usually do the pulls to match the cabinet so find a look you like on one cabinet and then use a ratio similar to that for the rest. LeeValley has these pulls in many sizes and are great value, you can order on-line and they have a good catalogue so you can get just the right size.

8 foot ceilings are normal. A few things to consider: Will there be a cabinet above? (If so, you need the kind without a chimney) Do the cabinets on either side go to the ceiling? (If so, that's good because you can bring your backsplash all the way up to the ceiling behind the hood so it doesn't look weird) Are there soffits? (If so, you have to make sure your chimney will even show, or maybe consider a built-in wood hood) Is the cooktop 30" or 36"? Neither is so huge that a hood will overwhelm the space. Pictures of what you have and what you like will help.

That sounds very nice. Before you invest in anything I would encourage you to make a sample board and think about how all these elements will look together. The grey of the cement floor( unless you stain it) of coarse your onyx , your white tub, your vanity, your tile, sink, fixtures, lighting, etc. be careful not to add to many dissimilar colors and elements in here if you want to make the onyx work.

Pulls from IKEA