You are largely correct.
Find Everywhere cannot be restricted. And it doesn't find really everywhere in RM. It finds most places in RM and is is extremely useful, but it doesn't find in all possible places you might wish to search. Also, some of the Find Everywhere searches give you little or no context about exactly where something has been found. Search results for citations are especially limited in this regard because you can see the citation but you cannot see the context of what person or event the citation is connected to.
Sources and citations can be searched indirectly through the standard search mechanism. But what you are really searching for are people, namely the people who have source and citation data corresponding to your search. You can search on the name you have given to a source. You can search on the source and citation notes (two kinds of notes for sources and two kinds of notes for citations) - memos in TMG parlance. You can search on footnote and bibliography sentences - on the sentences as they will ultimately appear, not the data that you enter that will make up the sentences. When any of these searches succeed, they will stop on a person satisfying the conditions and you will still have to search through the person by hand to find what you were looking for.
Boolean logic is available, but it is very incomplete. There is AND and OR but there is not a NOT, and parentheses are not available for multiple search criteria.
There is no way to force multiple search criteria (e.g., place and date) to be applied to the same fact. A search for census place containing Texas AND a census date of 1860 might return a person who was enumerated in the 1850 census in Tennessee and in the 1860 census in Texas.