An ancestor of mine came to this country from Italy with a brother around 1898. My ancestor was born around 1883; His brother around 1877.

By 1911, my ancestor was naturalized; His brother stood up for him as a witness, along with several men involved in the Junk/Metal trade. My ancestor is listed as a "Junk Man" in 1911, as is his brother, and other witnesses for his naturalization are listed as "Junk" men. By this point the Brothers co-owned a Junk store. My ancestor is listed on his 1917 Draft card as a "Junk Dealer", with the business listed as his own; The same goes for his brother. By 1920, he already owned at least one home, but was listed as a "Laborer", specificially in "Metal Work." By 1930, he and his brother had a falling out. He is listed as a "Plumber's Helper" on the 1930 census, but also owned a radio and three houses (the original house from the 1920 census, plus two others). His primary residence in 1930 was valued at $15,000, which is roughly around $200,000 now. He also owned a radio in 1930 according to the records.

The two main houses he owned were separated by a stretch of property, which included 8 car garages.

In order to bring the houses "closer" together, he bought the property and the 8 car garages and by the late 1940s was using the garages as a form of income, along with renting the front of one of his houses to a music store. He and his children (except for one) and their spouses lived in both houses. His primary home (post 1930) had been a Democratic Party house before he bought it. Thus he owned the three houses, the property and car garages, and some small property near one of his houses. He also grew his own wine.

His estate was apparently such that when he died, there was enough money to divide amongst six children, who used the money to buy their own homes.

I just wonder: Could there have been some Mafia involvement, or was the Junk/Metal work industry that lucrative? I just find it hard to believe that an Italian immigrant who spoke in broken English could become so seemingly wealthy in the span of time which he did so. Excluding the possibility that he came from money (which is possible but I don't know), is Mafia involvement possible or was he simply a very talented businessman?

Historically, some of the NY families have been involved in auto body shops, junkyards, etc. It's a good way to fence stolen cars, stolen auto parts, get rid of certain incriminating evidence, or whatever. In just the last decade, Carmine Agnello of the Gambinos was busted with several others for illegal control of the auto parts industry in Queens. And Fritzy Giovanelli's crew was busted for running a stolen auto parts operation in Brooklyn.

Extremely touchy to answer.
We do know that some Mafia members back then were fully legitimate people. There were lawyers, merchants, all kind of businessmen and even priest as fully initiated members.
Would you care to name your ancestors? I fully understand if you don´t want to.

Back then, you had to know someone to vouch for you over here, in order to move here. Or have relatives already living here. Besides that, when someone from Italy moves to the US, even today, they find their own kind. Always. More than likely, this was the case with your ancestor. They all seem to find each other and "help out" one another.

I love scrap metal, btw. Lots and LOTS of money in scrap metal. Juuuust saying.