Knocking though wall below chimney

We have a disused space in our kitchen where the original oil boiler used to be situated.
Its essentially a cupboard space made up of 4 brickwork walls, 2 of those a shared with the 2 internal load bearing walls of the property.
Above is a concrete pad, below ceiling level with the remaining chimney stack sitting on top.
The flue has been removed, and chimney capped externally and the bottom covered with concrete board.

Now obviously I realise I can't remove both of the brick walls within the kitchen without some structural work being done. However would I be able to just remove section of wall where the door is currently. Opening it up to a usable space, with the chimney and concrete still supported on 3 brickwork walls?

Also would anyone have any advice on how to make the concrete area above more visually appealing. Was thinking I could batten and plasterboard over?

Thanks in advance

Bump.

Anyone have any advice on how much we can remove without the need for structural support?