I can help you a little bit.

One of my professors (without revealing the name) is a rather prominent Carolingian scholar. Whenever he refers to Einhard in translation, he uses Dutton's translation. At the end of the day, however, you should ask yourself what the "best" translations will do for you. The Penguin translation that includes both Einhard and Nokter Balbus is perfectly serviceable to the more casual reader and is half the price.

Pretty sure the Oxford World Classics Bede is preferable to the Penguin one. That was the English translation we used in the Bede class I took when we needed to read sections in English so we could get to translating more important parts quickly. That said, if we came across a particularly difficult passage in the Latin, the professor would take out the English to demonstrate issues of of translation and talk about the difference between ours, his personal translation, and the published version. He also liked to mock the published translation...

As far as The Origins and Deeds of the Franks goes, my friends who do Frankish history usually refer to the Penguin version when looking at the translated version, but it appears that Murray did a version Yale's Readings in Medieval Civilizations and Cultures, which is probably the superior version, it's an excellent series. I would make sure that it's not abridged though, since it's simply called Gregory of Tours: The Merovingians. That said, Gregory of Tours is going to be confusing (by the original author's design) regardless of whether you read a good translation, bad translation, or in Latin, he's awful.

I think there's a free version of Jordanes on line. There appears to be a new version on Amazon, but I would make sure that's not a reissue of a rather old version. Jordanes is not as widely read and I would be surprised if there was a good version created for public consumption.

As far as Caesar goes, I'll let the others chime in with that, but be careful with any assumptions you make. Germans in Caesar =/= Germanics streaming across the Roman border several hundred years later. Similar, perhaps. Related, some of them certainly. But changed by several hundred years of experience and development, absolutely. Good read though!

I would also recommend reading Goffart's Narrators of Barbarian Antiquity along with some of these authors. Frankly, I would say that this volume would be of more utility to you than a perfect translation (whatever that would look like). For example, Goffart develops the idea that Gregory of Tours made his book confusing as hell and absolutely interminable on purpose to mirror the chaos that he was writing about. Long story short, Goffart will help you to see back the numerous layers of rhetoric in Bede, Paul the Deacon, Jordanes, and Gregory of Tours.