We had our 'dream kitchen' installed a couple of years ago. Here's my take:
Don't. Get. The. Rangemaster. It's absolutely shit, and my biggest regret. We have the induction top which is stupidly underpowered compared to the two induction hobs we had before. Big oven is insanely patchy on heat. Small oven takes about an hour to come up to heat. I wish I could go back in time, put a separate good quality induction hob in; and four eye level modern ovens set into a wall of cupboards, two either side of the hob. Why bend down to deal with burning hot things when you could do it at eye level - so much safer. Also the extractor - make sure it's higher than the tallest person in the house - my DH bangs his head on our every day and I'm pretty sure he's about to take a hammer to it.
Get the ovens with pyrolitic cleaning - saves a fortune & time in the long run - our Rangemaster is always desperately in need of refurbishing inside and out!
We also have a microwave / combi oven built in another wall - I was adamant I wouldn't have a microwave/ kettle cluttering up my surfaces. I can deal with a Dualit toaster and a Lavazza coffee machine and that's it!
Re the island - we kept ours free of the sink, so that it's about pleasure. We can also seat four-six, and the centre of the island is always filled with huge fresh flowers and smelly candles etc. For me, I wanted to keep the island for luxury / relaxing, and have all the operational parts in wall units. Mixing them just confuses the whole concept for me (although I know lots of people do it).
Under the island contains the wine fridge, natch, and a big cupboard for our many many cook books.
Re taps - definitely have a boiling water one, best new gadget I would never be without, saves so much time.
We have a water / ice dispenser in a big American style fridge, so don't need to clutter up the sink area with another tap - why create more going on there when you don't need to?
Sink is a large white butlers sink (next to a large capacity dishwasher), so not used for massive amounts apart from handwashing.
I do wish we'd added one of the multi-directional hose attachments - they look pretty useful.
Depending on how much wine storage you want - we had hand built wine cubby holes built in an arch over the double fridge and it looks amazing (demanding on the dusty front but worth it for me).
We have the deep pull-out shelves in the corner unit which adds so much storage, definitely have one of the rather than an awkward corner space which you can't reach.
Ours was hand designed and built to scratch from English oak, so we were able to specify wall units that go right up to the ceiling - looks much better and avoids those open sticky grim bits on top of cupboards.