It's important to remember first that, like with almost everything, all things concerning the nobility are subject to a lot of variety and change depending on when and where you are talking about. While there are many parallels between, say, German and English nobility, there are also many stark differences that shaped and continue to shape the lives of this particular social class to this day. Another (and very striking imo) example: We tend to think of the nobility as a small and very influential elite who assert their dominance by means of their social prestige, legal prerogatives, political power and large wealth. In some parts of Spain, however, the "hidalgo" class of nobility actually covered the majority of the population. In the Basque Country, even a "collective nobility" was instituted which meant that virtually 100% of the population there counted themselves as "noble".
That said, there are several hierarchies present in nobility. I will be focussing on early modern German nobility because this is what I know best, but I think that at least the rough outline should be similar to other areas and times.
The first hierarchy is the, for lack of a better word, "inherent" hierarchy of nobility. Not all nobles have the same rank; instead, the Emperor claimed to be the highest-ranking noble in all of Europe (a claim that sometimes even went uncontested), followed by kings, dukes, counts, barons (Freiherrn), knights, "noblemen" (Edle, although afaik this only existed in Bavaria and Austria) and finally even a group of title-less nobility, only marked by a von in their name. Each of these ranks also had a great amount of internal differentiation, with the Habsburgs for example outright inventing the title of "Archduke" (Erzherzog) in order to console themselves after not getting any of the coveted offices of imperial prince-electors in the 14th century.
The second hierarchy is that of age. Early modern nobles differentiated between Uradel, i.e. "ancient nobility" and Briefadel (nobility created by letters patent). The earliest example of a noble noble line being created by royal writ occurs during the 14th century, and it becomes a common phenomenon furing the Early Modern Era that meritorious bourgeois families get ennobled like that, often for loyal services rendered to the crown. There are also some types of "ex officio" nobility that appear during the EME, where being appointed to a certain office meant an automatic elevation to nobility. Officers in the Habsburg armies could (theoretically) claim such an elevation after thirty years of military service, and getting ennobled was also common for many higher-ranking offices withing the Catholic Church or other institutions. Lawyers at the Imperial Aulic Council also got the opportunity to become noble sometime during the 18th century, for example.
Another hierarchy was the difference between imperial and "landsässig" nobility. I can't find an English translation for the latter word, but it basically means that you had not been ennobled by and/or didn't swear fealty directly to the Emperor, but by and to your local prince. While your rank was (mostly) accepted everywhere else too, members of the imperial nobility (Reichsadel) tended to look down on those noble families who wear bound to a mere prince. An additional complication appears here, however: Receiving your letters patent of nobility by the Emperor didn't necessarily mean that you were reichsunmittelbar, i.e. swore fealty directly to him. There are some families that call themselves "Imperial counts" because they were ennobled by the Emperor, but they never were reichsunmittelbar and were therefore of no higher rank than landsässig counts, although they might be of higher prestige. Reichsunmittelbar counts also called themselves "Imperial counts", so you have to be careful there.
A fourth hierarchy would be that of wealth. Just being noble didn't mean that you automatically were rich, of course. This hierarchy wasn't officially accepted, but it existed nevertheless. Some noble families were much richer than others (there were indeed some noble families who basically were peasants with a bit of money) and therefore also had better opportunities to get involved in politics. Other hierarchies of power were possible, too, like the power attained by virtue of a powerful position within the Church, or the military, or at the Imperial court in Vienna, or at other royal and princely courts. There was also the question of social prestige, like when the status of your entire family was permanently enhanced by a famous ancestor. Asch defines the nobility as a "community of memory" (Erinnerungsgemeinschaft), and therefore what happened in the past could very much be a question of current urgency and power for later generations.
The Gothaisches Genealogisches Handbuch is the definite authority in contemporary Germany for all things regarding the nobility and its various ranks and hierarchies and the closest thing you will find for an "official" definition of what constitutes minor nobility. According to them, "high nobility" would be all ruling houses and reichsunmittelbar counts, whereas all others fall under minor nobility. As always, it is way more complicated than that, though. Wallenstein had come from an old, but not exactly well-off noble family (that they were poor is probably a legend, however). When he became the Duke of Friedland he was one of Europe's wealthiest and most powerful nobles for a short time, no matter the relative youth of his new title. The Fugger family were also part of the new "Briefadel", but their fantastical wealth made them into a powerful political player during the 16th century. On the other hand there are also high-ranking and old families that either had fallen on bad luck or never really made it out of there, and while they might not have been minor nobility according to the Gotha handbook, they very much were "minor" under all other aspects.
Martin Scheutz differentiates between five groups of nobility in early modern Europe, and I'll simply translate him here:
The Imperial Princes, the Magnates in Bohemia, Hungary and Poland, the British Lords, the Spanish Grandees and the nobiltiy at the French royal court constituted the so-called "old nobility", which owned and controlled large swathes of land and sometimes even was able to operate within several different countries.
In contrast to this "old nobility" you have the "rich nobility", which formed a regional elite and had property and income.
Most of European nobility can be regarded as a local elite that drew its income from their property and estates and could live in a way befitting their noble rank [standesgemäß], e.g. in a castle or a palace in the city.
On the other hand, there was a nobility almost bourgeois in appearance which led a modest life and was barely able to live standesgemäß, with only a few domestic servants.
At the lower end of the noble hierarchy was the poor nobility, which could only claim authority over a few peasants and had to live non-standesgemäß as 'Krautjunker'.
So, how did "minor" nobles live? In short it depended on a multitude of factors, and your exact location within the complex and ever-changing hierarchy of nobility didn't necessarily correlate with wealth and/or political power.
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Thank you!Ii enjoyed reviewing the titles on offer and the history of their creation.