Even trees and plants need to be researched. Some might not have existed then. Some might not have grown in locations where they are to be found now.

This is where things get complicated (as is often the way with religion). You don’t just have to describe religious practices. You have to get into the characters’ heads and work out why beliefs make them act and talk as they do.
In this article, Amanda McCrina claims that the vast majority of historical fiction mostly ignores religious practices and the pervasiveness of religion in people’s lives, making them more modern in outlook than they really were. This makes life easier for the modern writer and also makes it easier for the modern reader to identify with the characters.
Should you write your story in the first person or third person?
As with any narrative, your decision must be based on the type of story you want to produce. Third person lets you (and the readers) see situations from different points of view. With first person, you concentrate on the viewpoint of just one character.
If you choose the first person, you need a credible reason why the character should tell their own story. You also need to be sure you’re able to be the ears, eyes, nose, heart and brain of a character whose experiences of life are necessarily very different from yours.
I may have overwritten this point, but it seems to be one of the main facts about writing historical fiction. Information dumping is annoying, yet you need to set the scene and somehow make readers understand what life was like in those days.
So don’t include everything from your research notes, but do include enough for readers to imagine themselves there. Find the right balance.
One of the best places to go to for some in-depth researching is a museum. You can find answers to your questions from the exhibits, on information boards, from computer screens, audio guides or human guides. Displays often show how ordinary people lived. Libraries contain books that provide specialised information and museum shops sell books and objects that can help you reconstruct the background to your novel.

I don’t want to compile a list of all authors who write/wrote historical fiction – just those I have read and those I feel I ought to read.
I haven’t actually read a lot of historical fiction. These are the authors I remember having read:
Which other authors should I read now? Any recommendations?
Some writers prefer not to mention famous people. They write about the unknown people. That way, the characters are formed purely by imagination… and knowledge about how people were and how they behaved at that time and in that place.
Others purposely write about famous people. They leave themselves more open to criticism, because they can’t always stick to the truth, but we’d be poorer without their stories.