1. Same as ours, -ish!
2. It would become a conservatory? Ask EJ, amongst others. Don't know about a Rayburn, but an AGA in normal use costs £1.75 per day. It could be run on 'idle'.
3. Starting off?. Far too big. To heat the whole thing to 75-80F would be V costly. So, Exotics perhaps? Again - Emma.
4. Gets too hot for us on the 2 days of Summer!!
5. You were awake??
6. You would need easy come easy go shading as well. Even with 24 vents AND shading, we have a job to keep our big greenhouse down to the besr temperature.