I wouldn't put any water under there because of potential mould issues (in fact, there looks like there's a bit of mould already -- is there?). You could tile the bottom of it and put a strip of LED lights under the glass. What did you have in mind when you initially thought of the idea?

You list is all "stone" products. Stone products are natural. The durability is guaranteed with stone. Stain resistant...remove marble and granite from your list. Both can stain and etch and both will do this with "flooring" more than they will with a counter top. Gloss levels all change...but it will take years to do it. All stones have maintenance = homeowner needs to work at keeping stone looking good. Stone = expensive. There is no "benefit" for "reasonable" when working with stone. They all cost plenty of money. Stone is expensive. No way around it. If you want "glossy" that doesn't stain for a "good price" then you have forgotten to mention the BEST option: porcelain tiles. Porcelain will do everything you want for a lower price. Stone is expensive, it can stain (especially "oil" stains) it will "etch" or lose gloss level with certain liquids (acid based liquids will do this) and they all need to be maintained and eventually need repolishing to maintain "gloss". Durable is all you can expect out of stone. The rest of your wish list belongs with porcelain tiles.

As far as spacing between the pavers, you want a minimum of 3mm or ⅛ an inch, but the ideal spacing really depends on the whole space and how you want to fill the space between pavers. If you are thinking about pea gravel or sand, you probably want less space between to help keep your costs down and make it easier to power wash. If you are looking to add greenery then more space between the pavers gives you more green, creating a more natural-looking space. If you do decide to go the gravel route, you can apply a clear coat of something like gravel-lok. It acts like glue, keeping the gravel in place. It may not be able to take the full force of a power washing, but it will certainly hold the gravel in place better than not having gravel-lok. If you do want to go for a green option, grass could work, You could also look into small succulents, moss, or clover. With any green option, you will have a little more maintenance in the form of trimming and watering, but the look is stunning! You absolutely can put grass between the pavers. It will actually help stabilize and hold the pavers not move them. (if installed correctly) I would space it 4” apart and use netfin or a similar subsurface drip line to water the grass underneath the soil. This look is probably my favorite but you could also use a crushed aggregate in between too. Gravel is a terrible idea because it doesn’t stay in place. Here are some ideas from our projects of all kinds of paver designs:

Thanks One Plan for your recommendation. Would it be good to go for Herringbone pattern in hallway and in the open plan vinyl straight planks and then matching tile in the decking area. We have shortlisted karndean vinyl for open plan (Von Gogh Distressed Oak) althought not sure. Also what type of anti-slip material should I go for if I had to matching wooden look vinyl ?