I really don't see an issue with the rooflines. Looks like the angles are fairly similar and the clean lines of both structures should be easy to coordinate, especially in your open, rural setting. Since you've found a stunning deal, I would say, go for it! I definitely would want to find an architect ASAP and by all means, before you pour the slab, make sure you have a plan to coordinate.

Low ceilings = flush lights. Before you purchase carpet get 5 or 6 agents round to value. Ask each for their opinion on what they think will appeal best. Ask them if you could get away with just laying underlay. For the wow factor make sure your budget is spent on items that you can take with you - think a huge 6fx3ft mirror, a bright modern art print, a mirrored console table etc. No need to splash out much just one item in a room or two to indicate wow. A patio table and chairs in the garden are also needed for the selling photos as they will help the buyer to see scale and the garden will appear more homely. A bowl of fruit in a chrome wire bowl in the kitchen will also add wow - stage with green apples and yellow lemons for example. So, to sum up the spend on 'wow' should be limited and only to what you take with you. As for the estate agents some of them do try very hard to give good sales advice so when you book them to value explain that the property is being flipped and you would welcome any ideas on how to present it. You may be surprised at what they suggest.

Kind of funny really how many people would feel exposed and would not want to use the bathroom. The more I think about it, it's a bit like a public restroom with stalls (as stall walls rarely go to the ceiling or floor and have the added issues of gaps between the wall panels and doors -- which thankfully we won't have!). Regarding the humidity control issue, I should have clarified this is only for a toilet and small hand basin (not a full bathroom with shower). The main room on the other side of the proposed toilet is our dog whelping room where we will have young litters of puppies (when we have them). Further down the hall, removed from this room, is our training room where there are likely to be other visitors but the proposed bathroom would be quite removed from that area. It would be wonderful to find more windows like the ones that are up near the ceiling! That would certainly solve the issue. I'll have to scour the demolition/restoration places.

The all black kitchen looks scary as. Maybe because there's no lightness in there at all.