I learned from other people's gadget excesses, although it didn't stop the designer from screwing up. Lesson 1 is don't assume he can use a tape measure and double check the room measurements as well!
pretty happy with ours; drawers are indeed good although pricey. Glad we have no farty internal 'Le Mans' stuff, just wastes space. No integrated appliances except the oven, they cost more and have less capacity. Make sure designer realises that a 60cm wide freestanding appliance needs a space 65cm wide (stupid sod...) The worktops are a little bit too narrow, the same width as the cupboard so when you clear up crumbs they fall on the floor. This is another piece of modern stupidity but may be unavoidable.
Get a normal sink with curves - the rectangular ones are indeed designer crap that catch mess and are impossible to clean properly. No boiling water tap, have a kettle. Installer did screw up placement of taps a bit, didn't notice until too late. Pull out the aerator thing or buy a cheap tap without one if you can, they are just devices for spraying water about.
upstands cost a fortune. Tiles are much cheaper especially if you can fit them yourselves. If you have a gas hob the worktop probably won't be deep enough to allow a glass splashback, so you'll want tiles there too.
don't let a kitchen fitter do plumbing, make sure he gets a plumber in. Make sure all pipes have isolator valves that are NOT buried behind cabinets. Get raw edges of cabinets sealed (this was promised but then refused, we gave up and did it ourselves). Kitchen guarantees are worthless so think robustness and ease of maintenance.
no cupboard for towels; think about it, how will they dry? You would always be opening it with wet hands! Find a space for hooks. No over complex rubbish and recycling 'station', we have a bin and a crate under a worktop, stuff just gets thrown in. Life is too short for extra doors.
go through the design and cross out all the panels between units, £50 each and just waste space. Go through it again when the designer tries to sneak them back.
it's like arranging a flashy wedding (or so I believe) - they assume you have money to burn. Make it clear that is not the case.