I think if you were to have all the floors refinished, they could match a new floor to your existing. Have some good hardwood flooring companies come out and advise you. Personally, I would stay away from any dark floor, it will show everything.

I want to use Ultra pure white behr time color, so I can have some contrast but want to make sure the color hue family wont be off? Not off at all. Plenty of contrast in general but most importantly in terms of Chroma. Honestly, there aren't many colors Ultra Pure White doesn't work with because of its high Value and low Chroma. In a word, nuance. When we consider a color's lightness and colorfulness at the same time, that's called nuance and I think it's what makes UPW such a pretty color of white. Every brand (I think) has a color named Swiss Coffee. IMO, BEHRs is the prettiest. It's right on the edge of being an off-white and a light near neutral. I have a post about it here. https://thelandofcolor.com/swiss-coffee-12-by-behr/

I love maple floors IMO 10x nicer than oak. What are you planning to do for the flooring? Maple does not take stain well but I think natural maaple is lovely. Maybe paint the spindles of the railing black for a bitof releif. As for the island I think the whole 2 tone kitchen will be a dtaed look before long. I like simple so I would leave it alone .Make sure all your light bulbs are LED 4000K before choosing anything more . I think add a huge bowl of fruit on the island and thats it . I would also look fror some art that is a little more interesting and no staggered hanging of art on a wall.If you do not have lighting in those glass cabinets add some also LED 4000K I would also do some stools at the island that do not match the oters but something colorful

I just read about Ahern White - https://patrickahearn.com/blog/ahearn-white-paint-secrets-revealed/ Very interesting. Pics of it are stunning, though I noticed that every single one uses it with a different sheen on the trim. It seems like it was created specifically for really open, simple looking spaces that lend themselves well to a fresh paint without detail trim. That said, you can do whatever you want! I looked up on the Benjamin Moore site both of the components of Ahern White to see their matching and varying shade colors. Linen White: Clay Beige and Woven Jacquard. China White: Collingwood and Classic Grey. Perhaps these would be a good starting place. If they aren't perfect, go with a few shades up or down on the color card. I never look at instagram but see in a lot of UK homes trim that is darker than the walls. It can look stunning. Houzz is certainly a place that is more about American decor trends and folks here are not often keen on going outside that box so you may have better luck seeking advice elsewhere.