for handles, take a look at Ironmongerydirect.
Economy kitchens don't always have matching décor panels on the sides and backs of cabinets where they can be seen. It particularly shows with wall cabs around the cooker. They can be ordered from the kitchen co (overpriced) but you haven't got to go to a kitchen co. There are online suppliers at less than half the price who will make whatever you want. It all comes from a factory anyway. There are no grey-haired cabinetmakers sawing and planning by hand.
trims and cornices bring the edges, tops and bottoms together.
To my eye, a gap between the top of the wall cabs and the ceiling looks unsightly. If your ceiling is not very high, 900mm tall wall cabs are available in most ranges and will look better. Otherwise have it boxed in.
The worktop will be used and looked at every day. Again, it doesn't have to be bought from a kitchen showroom.
In-cabinet accessories by Blum or Hafele are usually marked up by the showroom, and are widely available elsewhere.
If you can afford it, don't get vinyl-wrap doors, which peel.
Never buy appliances from a kitchen co.
Ask around for personal recommendations of a local fitter, and look at their work first.
Have a plumber and an electrician do their bits before the kitchen fitter comes.
If you are hard up there are lots of ex-display and discontinued but new cabs and accessories on fleabay. Second-hand is very cheap because most people haven't got a van. Consider hiring a Man With Van to shift it and you may get a terrific bargain.