I love reading about the ancient Greeks and Romans but I can't read direct sources, but want to. I am just a fan of history, not formally educated (in history anyway). I find a have a massive common knowledge problem. It seems every page has multiple references to things (ex. cities, family names, ethnic groups, etc) that I have to look up. It's especially hard when I am suppose to know that that thing has a trait (ex. specific type of priests, political family, nomadic raiders, etc). It makes for difficult reading and I just go back to re-reading my favorite books about the ancient world. Thanks for any recommendations!
I'm a little confused, you're looking for modern translations of classical texts that explain references in the text?
If that's the case then you're in luck because there are a lot of very good critical editions of classical texts which have extensive notes that provide exactly what you're looking for. It's hard to point to a single one simply because there's so much out there. For example, if you wanted to read Herodotus, the Landmark Herodotus might be exactly what you're looking for. For the Republic you might try Bloom's translation and so on. I'm sure if you ask about specific texts (or even just specific topics, philosophy, history, plays, etc. that you're interested in) than you'll get a lot of great responses!
Absolutely, keeping your Messegetai and Scythiae straight is difficult for everyone. What you will want is the Landmark series edited by Robert Strassler. The series so far includes Thucydides, Herodotus, Arrian, Xenophon, and Polybius to my knowledge, and as this is quite a new series there are certainly many more on the way. They are scrupulously annotated an include many maps, illustrations and background information.