have a fused switch, 200mm above the worktop, at every point where you have, or one day might want to have, an appliance beneath. The fused switch to feed a single unswitched socket below the worktop.
Have a double socket at least every metre along the wall, 200mm above the worktop.
Get a proper electrician who is a member of a self certification scheme. Kitchen fitters are not proper electricians or proper plumbers and are notorious for shoddy and non-compliant work hidden behind the cabinets.
YYY to putting the flooring down before the cabs, it will protect against spillage and wildlife
YYY to cabs going right up to the ceiling. If you are too short to reach them, they will still fill up with your sandwich toaster, granny's best china, disused slow-cooker etc but will look neater and easier to clean
For your wall cabinets, have hanging rail fitted all along the wall. Cabs can then be lifted up and hung on it. You can reposition them at whim; it is very strong; and there is never a problem (as with individual brackets) of having a crumbly bit of wall or an electrical cable where you need to drill a hole.
Be sure to get a cooker hood that actually extracts the steam and greasy fumes through the wall instead of just blowing them round the kitchen.