Germans seem to have originated in Germany and southern Scandinavia, and have been there at least since Roman times. They also began to move eastward during the 2nd and 3rd centuries (IIRC) across Poland, the Carpathian basin and the Ukraine.
Huns? Nobody knows where the Huns come from. Or really much about them at all. Generally they're believed to have migrated from the steppes, but nobody is sure where in the steppe the originated from. The traditional theory has been that they're part of the population of the Xiongnu Empire (a proto-Mongolian tribal confederation) that migrated west after the empire was destroyed. Other theories are that they come from the western steppes originally like the Magyars etc or that they come from the very distant lands of eastern Siberia near the Lena river, to name just the two most geographically-distant locations. They are a bit of an 'Atlantis' people really.
Bulgarians are rather odd. Modern Bulgaria is a blend of Slavic, Ottoman Turkish and Greek influences, much like the other Balkan countries. But the people who the country is named for, the Bulgars, were originally none of those things. The Bulgars were steppe nomads from Ukraine and southern Russia, a region that was called 'Old Great Bulgaria', and may have had their origins as one of the Hun tribes. The Bulgars migrated in two directions. One group of them took the traditional route to the southwest into Europe, where they created a Bulgar Khanate, the First Bulgarian Empire. This Khanate became a Christian Kingdom and was heavily-Slavicised, and eventually was conquered by the Byzantine Empire. Incidentally, the First Bulgarian Empire was where the Cyrillic script was invented. The second group of Bulgars did something very odd for steppe nomads, and migrated north into the fringes of the Taiga, where they created the country of Volga Bulgaria. The Volga Bulgars were converted to Islam by Muslim merchants and missionaries, and remained a semi-influential force in Russia and the western steppes until their conquest by the Mongols.