Wow, what a lot of comments. I think you have a wonderful kitchen, which has been created with much love & attention to detail. You are asking about painting things in a dark / inky colour - & your Oak unit - but you already have a mid grey wall surrounding the Oak unit - which is why it stands out - take the walls back to an off white & it will blend back in. The lighting in the entire area doesn't seem to be enough for "dark inky colours" - If you really want something like that why not create a picture of what you want on canvas & put it behind glass in the Aga alcove? Your Aga is dark already so it might just make that area a feature. Don't start taking out bits of the kitchen - once you start you will carry on & suddenly your Dad's work will be destroyed, which would be incredibly sad. Your kitchen works well for you - I do agree that the floor could be underfloor heating with tiles on the top - but weigh up the costs before you start. Lighting is everything, so more lights - ceiling not spots -LEDs as many as you can! From the photographs you provide it looks as if the room leading off from the dining area is already a darkish room, & were you to paint the oak any colour at all I think you would regret it - a slight chip there or a knock here & the paint starts to come away - wood is beautiful, it holds history and it gives such beauty - use that as your palate.. Be gentile on your kitchen - try painting paper and then bluetack it to the wall / unit /island etc. so you get an idea of what it might look like if you painted it - a great source of long paper is to be found in the wallpaper isle - you can buy a roll of lining paper for under £5, get the paint test pots & try out your ideas without damaging the beauty you already have.

I can't do pics as my house is a mess but I have bought beautiful things from ebay and local forums for silly money. We got a huge L-shaped velvet covered sofa from Restoration Hardware for £300 inc delivery (near perfect condition and would have cost over $5k new), a huge solid wood apothecary coffee table also in perfect condition for £75, an occasional chair from Crate & Barrel (also perfect) for £90. Literally thousands of pounds of furniture for less than £500. I look carefully for things that are poorly photographed or ill-described as these often get overlooked. However, recently I was helping my in-laws sell some of their furniture as they were downsizing and I couldn't believe how hard it was to sell. They had bought everything 10-15 years ago from Harrods (eek!) and it was all in perfect condition and extremely well made, and in the end we were selling things for prices similar to the above which seemed such a shame. One other tip is to look at the sofa.com microsite on ebay - they have great things at very good discounts and they are available immediately.

If you take the 290 unit off the back run and island, I think that would be sufficient? As you've got kids I think a banquette seat would be ideal for family games, homework, crafts etc. Banquettes are around 60cm, table 90cm so that leaves 113cm which I think is more than sufficient both visually and practically as it's the same gap I have behind my kitchen table. Choose chairs that push under and consider the table legs carefully depending on the number of chairs wanted, pedestal tables often work. I would however take the sink off the island and maybe install a prep sink instead so the back run would be DW, sink, bin, induction hob (I'd integrate the oven personally). Is the shower room a must? It seems quite a trek to reach there with the number of doors unless there was a way to extend the 2nd front door forward and create access from the hall there. Also wondering if you'd considered removing the wall between snug and the old kitchen? It may make the area more useable rather than trying to fill the old kitchen

... also, i should add a caveat - the kitchen is still being rennovated - as you can clearly see by the fact that we don't have lamp lights above the sink, just wires - that's not the finish ;D (The kitchen pendants above the sink are these ones: https://www.industville.co.uk/products/brooklyn-glass-cone-pendant-light-7-inch?variant=9994088837&gclid=Cj0KCQjwxJqHBhC4ARIsAChq4atiHbRuKl-1YwIt2EIWwK8W3YdupQJD53iIkLCwvJR-gEpO6BbRnZcaAnO6EALw_wcB i.e. holophane style glasss little pendants x3)