Leonardo's father Piero was a successful notary, his money didn't make money like the super-rich so he still had to work for a living, but we can safely place him in the upper-middle-class; he inherited his notary's practice from his father and he supported Leonardo through his life.

Leonardo's mother was certainly lower-class (it's been hypothesized she was a domestic worker in the da Vinci household) but his dad and grandfather had his birth notarized (with something like ten witnesses) and baptized him as a member of the family and household, they never considered him anything less than a family member.

Leonardo's schooling was haphazard, it was entrusted at various times to his grandfather, his uncle Francesco, and the local parochial school. However, the erratic schooling was more the fault of the young artist than any trouble at home, wrote Vasari: "he began studying many things [...] and then abandoned them" and once his father gave up trying to teach him to be a notary (probably on account of his incomprehensible handwriting) he then hired a tutor to teach him math and an abacus (probably to prepare him to become an accountant) but Leonardo proved even less adept at this than he was at notarizing.

Luckily Leonardo's dad Piero's career as a notary was really taking off; while Leonardo was being schooled in Vinci, Piero had moved to Florence. Piero da Vinci eventually managed to get Leonardo enrolled as an apprentice in the painter Verrocchio's workshop.

Once he starts his work as a painter, Leonardo certainly was never poor or anything, but he definitely had a whole bunch of lucky breaks. There's a weird four-year "blank period" immediately following his breakthrough successes in the 1470's in which there isn't a trace of his work so we have to assume his father was supporting him. When he starts painting again, his work ethic which had been bad when he was an apprentice gets even worse; he starts some works without finishing them, even taking commissions without even starting them.

Somehow, Leonardo entered the circle of Lorenzo de Medici (maybe Daddy introduced them?) who was the behind-the-scened ruler of the Florentine Republic. He took up small-scale architectural drafting, but we don't know when he started drafting military machinery. We can only hypothesize that his boredom with painting had (perhaps starting in his period off the grid) given way to other pursuits. Was Lorenzo more interested in his drafting or painting? We don't know. What we do know is that in 1482 Leonardo da Vinci traveled to Milan with a golden lyre officially to take part in a music contest at the Milanese court, but unofficially to deliver a nine-paragraph letter to Lodovico Sforza.

You see, Lorenzo's diplomatic modus operandi was to contrive, outside of the normal appointment of ambassadors, the employment of Florentine artists (normally painters) on projects commissioned by his allies. King Ferdinand of Naples, for example, had two Florentine painters working for him, while a group of painters had also been dispatched to Rome. This tactic got Lorenzo in everyone's good books, plus when he wrote to check up on how his dear artist friends were doing he could, by extension, find out what was going on in rival courts.

Leonardo's welcome in Milan was tepid, but he seemed determined to adapt quickly. While at first his rural Tuscan accent was a barrier to making headway in the Milanese court, even his personal writings would soon be peppered with Lombard-isms. He had been awkward and passè in the refined and lettered Florentine high society (he would bitterly describe himself a "man without letters") while in the Milanese court his military imagination was fueled by the veterans Duke Galeazzo Maria's near constant campaigning and the uneasy peace over which his successor Lodovico presided. Milan had been bullying other cities in Italy for some two hundred years, this was the prefect environment for an aspiring military engineer. The ruling House of Sforza themselves were a cadet branch of the House of Visconti who had distinguished themselves as military commanders before Francesco Sforza came to the throne by marrying Duke Filippo Maria Visconti's only child and daughter, Bianca Maria.

Leonardo's bread and butter continued to be painting, although his multidisciplinary distractions continue to be problematic and start to drain him financially : He writes candid letters to the Duke Lodovico which can often be summarized with, "Give me more commissions!"

What were his living conditions like? At first he had lodged with two fellow artists in a workshop near the Ticinese Gate, but by 1485 he had his own workshop with three apprentices, a servant and a housekeeper.

Leonardo maintained himself primarily by painting portraits, but also slowly earned engineering commissions, first of which involved the city's canal system. He was sent multiple times to Pavia to oversee stones being cut for the city's cathedral (where he also took the chance to read up on anatomy at the university). He built an elaborate model of the Solar System for the wedding of little Gian Galeazzo Maria Sforza and Isabel of Naples, as well as plan an absolutely massive equestrian statue of Lodovico which was never built.

So I would say that overall Leonardo was on the better off side, although his distractions sometimes drained him financially.