I would like to cover the Kitchen Worktop, in my camper with a single layer of carbon cloth and hi temp laminating reason.

I was intending to use

Carbon Fibre 2/2 Twill 3k 199g

Very High Temperature Epoxy Laminating Resin 500g Pack

I have done a few structural repairs with carbon before but that is it, so I understand how to lay the fibre and resin, but I am looking for advice or a guide on how to get a flat gloss finish, ideally a mirror like one.

You're going to have to do some flatting down and polishing. You'll never achieve a perfectly flat surface through application alone. I would recommend getting an orbital sander with some fine sanding discs, say up to 800. Get it flat with 400 first, then move up to 600 and then 800. Then continue with wet sanding by hand up to 1200 or 2000 grit, then compound. 

the worktop is 0.5m2, but nearly half of the space is occupied by the stove/sink, so if I get enough resin for 0.5m2 that should be plenty. How much area will 500ml cover?