Your looking at labour costs of £150ish per day or around £20 per hour for a professional, ask around and get 2-4 quotes, try and get a look at some of their work.
Without being their I would suggest 3 days of work for prep/undercoat/finish coat and all the climbing around.
Best of luck
Have a look for micro fibre roller sleeves 9", Hamilton do a good one. Leaves a good clean finish. Probably B&Q or Homebase. If you have a local professional decorators trade store near you then Wooster pro dooz short pile (will need a Wooster frame for this). Use a good synthetic brush for...