I would say that if you’ve got this far(looks good btw) and own a jigsaw, drill etc, Then the cut out is straightforward:
-Ghost fit w/top to fixed/level base units.
-Check hob placement isn’t directly under any electrical points or too close to wall units(There is a recommended distance somewhere on t’internet)
-Hobs will usually come with template. Measure, dbl check, mark out perimeter with dbl thickness masking tape. Set masking tape to the inside of your marked perimeter. Mark internal lip on tape(allowing a couple mm tolerance).
-Four 9mm holes drilled on the inside corners of marked cutout guide.
-Carefully join the dots with your jigsaw. Use a lam. specific blade or a medium toothed metal work blade(cheaper, just as effective) most jigsaws have an oscillating function to help push through cuts. turn this off and use a med-high speed setting and guide rather than push jig. through.(If you felt you needed to, could clamp a level to outside edge of jig. foot plate to aid straight cuts)
-Support cut out with timber or human. Any high spots can be sanded etc.
-Seal cut edge
-Be mindful that w/top(esp. composite) will be very weak at cut portion
Hope this helps
Re. 4mm tolerance. Can you live with it? Or will it bug you. Did cut sides come laminated? If not would bring either side out a mm or so?