Definitely fiction. Downton Abbey creates a fictional world with made-up characters and events, although it may draw inspiration from historical periods and social contexts.
One idea could be a fanfic about a servant's secret life outside of Downton Abbey. Maybe they have a hidden talent for painting and are trying to make a name for themselves in the art world secretly. Another could be a story about a forbidden romance between a member of the Crawley family and a local villager that goes against the social norms of the time. And also, a fanfic about how the Abbey copes during a particularly harsh winter with shortages of food and fuel could be interesting.
There might be. You could also check some dedicated Downton Abbey fan forums. Sometimes fans share their own written fanfics there, including those with gay themes related to Thomas. However, the quality can vary greatly, so you may need to sift through a bit to find the really good ones.
Yes, there is. The 'Downton Abbey' novel offers a deeper exploration of the characters and the world of the famous TV series. It delves into the lives of the Crawley family and their servants in more detail, allowing fans to further immerse themselves in the story.
Fiction. While it draws on historical context, a lot of the specific storylines and characters are fictional. The relationships between the Crawley family members and the servants are often dramatized for entertainment. The individual dramas, like the love affairs and family feuds, are mostly made up to create an engaging plot. For instance, not every aristocratic family had the same kind of family secrets and romances as the Crawleys in the show.