The charring of wood as a method of preservation is nothing new and was known to European and Mediterranean builders as well as Asians. I have for years charred the bases of deck posts and such as a rot preventative. The practice is mentioned in John Fitchen's classic book Building Construction Before Mechanization. Some of the samples of this shown above are a bit crude. The most beautiful finishes of this type are rather labor intensive as some of the char can be brushed back off to some extent to reveal wood grain. The planter shown below has been coated on the interior with linseed oil, blackjack and turpentine and then set alight with a roofer's torch. The finish is cooked into the wood producing a carbonized insect and decay resistant surface. It gets filled with soil and so the char will be seen only at the edges.

I would leave the render colour and just tile a trim around the base in a pattern and over the arch of the brick. But I also recalled the pizza oven at a pizza place where I grew up. They make great pizza, but the oven is so cool! You could do something like this!

Huge thank you Moss Furniture .Your furniture looks great !

I know you said that you don’t want to paint the brick but between the ceiling, brick and paving there is just so much brown hard surface which will work against your goal of a cosy feeling. Do you need to keep it fully roofed? I’d suggest some outdoor rugs, in a lighter colour, to define the seating and eating areas. Timber or wicker furniture def no glass or metal. And a lot of plants and greenery. To get comments of layout you need to post a sketch of the floor plan of the space with measurements.