between the door and window looks about 3m so you would need a 3.5 catnic lintol to do this, would take 2 men about 2 days to complete with plastering, not sure on cost as rates vary all over the country but the lintol would be £200-300
you could try some rustic looking paving slabs 450x450 side by side these can be quite effective, point the joints and paint with waterseal to seal the top
you can point your bricks as you are going with the same mix 5-1 , just a splash off plasticiser is fine in a small mix, if a cavity wall there is no need for waterproofer
i might be wrong but are new houses pressure tested now? i built some last year for housing association and these were pressure tested and passed with no problems
bonding in theory should start in the footings and continue up until the job is complete, having straight joints between damp and footing is not correct.