any ideas for house improving?

Thanks Gwiniel, I am during introducing of your advices, it was quite sad to delete all these rooms that I previously copied to fill each floor, but it's only my fault because I overrated my computer possibilities. Although it's also more playable after making more space on my SSD drive and removing some unused software, but still my task manager shows that only 30% of CPU and RAM was used during performance drops (worst were during making new room or painting walls) so I don't know what is happening with other 70% of my computer's power. I deleted objects from rooms and used black wall/floor painting so it's impression of lights turn off, also it's easily visible that particular area is finished and not developed further, instead I kept one room of each kind and will try to make these more detailed. I deleted half of lights sources, it's darker than I wanted, but most likely has positive impact on performance. Broad corridors look better:) thanks for your kind words about house, although from what I see above, even castle would be not good word:D I will keep on deleting repetitive areas and developing these that can be made unique in some way. Would be great to read more good advices like above:)
A grade areas after deleting rooms

Kitchen for owners and A grade guestrooms (my sim went there to use fridge, although they have this one for 14k $ in their living room:D )

B grade dining hall after reducing number of lights, chairs and tables

how it started - terribly look of same house from one of early saves (23 december 2018) :)