Finish decorating first ,you may see that it doesn't stand out so bad...once your landlord see's how you update and help the looks of the place he will be even more eager to let you paint if needed

I'd presume the combustion fireplace is a built-in unit. I remember ours heating the bricks up quite well. I don't see an issue plastering the brickwork but look to use 'Fyrechek' which is a fire retardant plasterboard. The bricks could also be rendered instead but I reckon you'd be able to pick the different surfaces once painted. I wouldn't think you'd need a heat resistant paint. The walls would be warm but no warmer than a wall copping direct summer sunlight.

I'll stick my neck out and say I love painted brick, especially when not in overwhelming proportions, so I think your house would lend itself well to this treatment. I can see the brick on your house painted in Surfmist - I believe it would totally transform the feel of your house. I love what you've done so far. If you do paint the brick though I would paint the garage door the same dark grey of the wood trim. Jon n Kate Miller are right - if you paint brick you have to be committed. Also don't take short cuts on surface preparation but if done properly there's no reason it shouldn't last as long as any other painted surface.

we had a similar dilemma and couldn't find a suitable heater for the small space and regretfully made the decision to block off the old fireplace (there's now nothing visible as the chimney was outside the wall and the original mantelpiece was long gone) and we now have a boring very efficient gas heater with underfloor power flue BUT i'm now advised by my sustainable building designer that the latest electric space heaters (with suitable insulation) are more efficient so it could be worthwhile to research an electric flame fire for the ambience in the old (sealed chimney) fireplace and reverse cyclce airconditioner for temperature control...