Yes, this factually happened in the Classical Era.
Medieval feudalism began in Germany long before the fall of Rome. Before Rome first invaded Germania, Germany was made up of many small iron-aged tribes where warriors would swear loyalty to their chieftains. However, when Rome began to threaten Germany, these chieftains began forming larger kingdoms by swearing loyalty to one another thus forming the original prototype for medieval feudalism.
So, this system already existed in Europe a few hundred years before the fall of Rome, and they existed as next door neighbors as it is in your setting.
As for your specific details
Lack of Roads: This will be a big one. A lack of roads was a major reason that Rome struggled so much to conquer Germania because their legions had a hard time traveling en masse in the overgrown Germanic forests.
Landed Peasants: This will not be the slightest bit surprising to a classical civilization. Most classical era populations were anywhere from 50-90% slaves. The average medieval peasant actually had more authority over where they worked and who they worked for than the average Greek Helot, Roman Servus, or Egyptian Sqrw-anx. The most surprising thing to a classical person would actually be the lack of task masters. In most classical civilizations, the lowest members of society worked under armed guard to make sure they did not rise up or run away. The fact that serfs were not freemen, but could be trusted to stay and work in one place out of a system of pure honor would be the only surprising element of landed serfs.
Other major differences to consider
Literacy: Most people in the Classical Era had at least a basic level of literacy. Written language was everywhere including store signs, financial records, libraries, etc. However, Germans, and many early medieval civilizations that followed had very little literacy. A Roman would feel at a loss in a civilization that keeps financial records by carving tallies onto sticks or than does not not have any labeled shops. Instead the Germans maintained everything through oral traditions; so, the prominence of bards who could recite history and other knowledge verbatim would have likely been fascinating as well.
Law: Germanic Law was much more simple than Roman Law because there was no Senate or Written record of laws. Instead Germanic culture, as well as many early medieval cultures maintained order almost exclusively through arbitration and tradition. So, a Roman would likely struggle a lot with the idea that nothing is technically illegal, but "being a ####" is still punishable if someone calls you out on it.