IMO you are ahead of yourself . First the floor then if you eed wallpaper it needs to work with the floor and same for metal choice these all need to work together before doing anythting . Grays ae difficult to mix so that is the first item to deal with . The cabinet is set so now you need to see what flooring works with that gray . Do you have the cabinet? For me I would think cement tile for the floor , no wallpaper just a nice color from the cement tile for the walls this is just one of 100s of cement tiles you can choose from I like this since then go chrome for the faucet and that dark blue for a wall or if you have great lighting all the walls dark blue. Powder rooms are where you can have some fun they really can be like a little world all by themselves

There's nothing wrong with what you're considering except it will end up looking rather bland. You should consider doing at least one of the things Patricia suggests, either livening up the floor or the walls. If this is too adventurous for you, when everything is in place, invest in some artwork to liven up the space. Wicker accessories are good for adding texture and colored hand towels would help too. No one spends a lot of time in a powder room, so a lot of people use colors in it that they wouldn't use anywhere else. I got these wonderful pictures of peacocks and two small landscapes and then chose a blue wall color that went with them. Everything else is pretty basic. Everyone loves the peacocks. :-)

I love grey, but this is overkill.

If you are completely in love with this vanity and wallpaper, then I suggest white for the floor tile, something simple since the wallpaper is going to have a crazy pattern. Like large hex tile, not small.

Then plan on getting a few colorful things in there -- towels, shower curtain, plants, countertop accessories, etc.

Thank you all for wonderful insights!

@Patricia Colwell Consulting: May I know the exact name of this patterned tile you've suggested? Thanks!

Here is another option I am exploring with Ikea Hemnes vanity -

1. Wallpaper - https://www.homedepot.com/p/A-Street-Prints-Labyrinth-Pewter-Geometric-Paper-Strippable-Roll-Wallpaper-Covers-56-4-sq-ft-2540-24003/301232267

2. Tiles - https://www.homedepot.com/p/Lifeproof-Carrara-18-in-x-18-in-Glazed-Porcelain-Floor-and-Wall-Tile-17-6-sq-ft-case-LP501818HD1P6/308500675

something that will look like - (Raw design alert. Kindly ignore Hemnes top cutting)

Could you please share your thoughts on this one? TIA!

I don't mind the tile and the vanity together - I would start there and wait on the wallcovering and paint colors until everything is installed. I think there are potentially better choices for wallpaper - that is a lot of grey and you may want something a bit more interesting/lively once the fixtures are in place. For wallpaper - I would look further afield than Home Depot, places like Hygge & West, Spoonflower, Chasing Paper, Anthropologie, as well as Graham & Brown have lots of amazing choices.