Rather than use the custom tab that Mike is describing, I have a different approach.
When a new database comes online, or I start a new line of inquiry, I create a Named List for it and add to the list the names of the individuals I want to search for. As I find them in the database, I take them out of the Named List.
Here's an example: certain census records in the USA record information about whether anyone in the household is a veteran and some say which wars. After entering the census with Ancestral Sources, I go into Family Historian, turn on Auto-Source citation, and add information beyond the basics that AS doesn't help with. If I find a veteran of the US Civil War, I can add that person to a Named List of Civil War veterans, and as I work through individual databases, I can make separate Named Lists for those. So I might have a Named List for Confederate Veterans who served in the state of Georgia so I can look for their pensions in the digital collections at the Georgia State Archives (the 'Virtual Vault).
Mike may say this is not necessary, but I sometime create
Genealogy Source Checklists like this one demoed by Crista Cowan at Ancestry when I am working a
specific research question because it helps me review the data. I do not create one for every person in the database -- they are only done when I need to do a review, and am looking over what I have with a specific question in mind.
Before entering sources into Family Historian, I often create projects in Scrivener, the writing studio software from Literature and Latte. This is especially helpful when I am sorting out records from multiple people with the same name, and I'm not sure which records belong to the person in my Family Historian database.
I appreciate all the resources Family Historian has to offer -- the plugins, the custom facts, etc. -- but sometimes for my own thinking process, I have to work outside of it. As time goes on, I am trying to approach my online searches in the same way I would do a search at a repository offline, so I need my To Dos organized by repository and record group as well as by individuals or families.
My rule is "do what works".