Short answers, pulled from the story.
The Lex Claudia forbade Roman senators from owning a ship larger than three hundred amphorae. This legal restriction created a complex web of economic behavior for the elite while officially barring them from direct trade to preserve their status.
Senators and their sons used freedmen like Quintio or proxies such as Cato the Elder who employed fifty other men to manage commercial interests on their behalf. These arrangements allowed wealthy men to diversify income without violating the letter of the law.
Harbors at Civitavecchia, Ostia, Portus, Leptis Magna, and Caesarea Maritima stood as substantial remains of this commercial infrastructure. Monte Testaccio served as a physical tribute to the scale of this maritime commerce within the city itself.
Gold coins of Claudius excavated in South India provide tangible evidence of this long-distance exchange alongside hoards of Roman currency found throughout southern India since the history of Roman-India trade began. Ports on the Red Sea coast of Roman Egypt connected directly to destinations on the Malabar Coast of southern India using monsoon winds.
Negotiatores acted partly as bankers who lent money on interest or bought staples in bulk quantities while Argentarii served as agents in public or private auctions who kept deposits and cashed cheques called prescriptiones. These figures functioned as moneychangers and kept strict books called tabulae which courts treated as legal proof.