A tile backsplash can wait and may be easier to visualize once the other components are in place. For now, decide whether you want the granite or not since it would be difficult to match later from a different slab. Subways have been used a lot recently. You might want to explore other shapes and textures for a fresher look-easier to do when you're not feeling rushed.

The lighter travertines are white-pale gray-ashy beige. Your floor will probably need stiffening to prevent cracking natural stone tile. There are some decent porcelain look-alikes that would be less fussy about installation.

If you plan a tiled backsplash in the future, then I would not get the short granite backsplash...it'll save you $$$ now and it won't be a problem later when you want to remove it to put the backsplash in. If you wait a while (like we did), then just paint it w/a scrubbable paint and be sure the crack b/w the wall & counter is sealed.

It's a lot easier to "visualize" a backsplash once the cabinets, counters, floors, etc. are in...so I wouldn't worry about it if you don't know what backsplash you want right this minute.

Would not sweat the backsplash now either, and without seeing the plan or the style cabs, think that Subway tiles may look busy and detract from the granite (due to lots of grout lines)...large tiles or travertine might be better. Also where and how close to high abuse (stove back, sink) areas are the back splash areas
For floors, dont dismiss natural wood colors, such as bamboo. My SIL did her kitchen in dark mahogany cabs (upper), stained some of the base ones a sage, put in granite, and a light wood bamboo floor with enough brownish veining tones in it to compliment the mahogany. The light floor makes the mahogany pop without feeling dark and her touches of color show well as a result.
The bamboo flooring can hold up fine in a kitchen but perhaps not a high traffic with 4 kids. We have wood parquet (highly sealed) in our kitchen which gives a light maple glow with st steel counters and dark cherry cabs. That has worked well too and last 20 years. I like the wood as it is forgiving to stand on and work. And fewer things break if dropped.
Good luck.

You mentioned that you really liked black slate. Have you looked into other colors of slate? Slate comes in a huge variety, including grays and variations of gray and other colors.
Daltile Slate

There is also quartzite which (to me) looks a lot like slate.
Build Direct Silver-Gray Quartzite
Amazon.com Ostrich Grey Quartzite

Also, I believe limestone can come in a more gray (less beige) color. See the Arctic Gray (or even the St. Herbert).
Daltile Limestone

(Disclaimer: I am not affiliated with any of these websites, nor have I purchased tile directly from them. Just wanted to show you some non-black, non-beige stone options. I did see a lot of Daltile slate when looking for tile for a bathroom. I really love the look of slate and quartzite and hope to use one or the other when I get to my kitchen project.)

I don't think of specific floor stains as getting "dated" in the same way that certain cabinet stains do. Unless we're talking about red oak flooring with a TON of very heavy, dark, and wide grain... In that case, stick with something medium. Otherwise get what you like.

Personally, if choosing stained wood cabinets, I prefer floors with contrast. Since you're going dark on the cabinets, I'd go many shades lighter on the floors.

Here is a link that might be useful: Our Bungalow and Kitchen remodel blog