I would welcome more info on this line. I can offer some, especially with regard to the banking though I don't know of the NY connection you mention offhand.
James Humes was involved in founding Swatara Bank with a James Hamilton and others. This is referenced in PA Archives records. I suspect one of the best sources for more info on the business activies of the Humes and Hamliton lines are likely to be found in the White Chimneys microfilm at Lancatser County Historical Society. These are from the Slaymaker family, which handled legal affairs and had some marriage connections to the Humes and Hamilton lines. Account books related to Humes and Hamilton families are found referenced in the indexes to these and there is a James Humes Slaymaker and I think one named for Hamilton also. I found more on the specific connections once but don't have the info handy, and I didn't get a chance to check the Slaymaker microfilm the one time I made it to Lancaster yet but after finding the James Humes Slaymaker reference I wish I had and I suspect that ti could be a good source of more info that has never been published yet. I think there may be another later James Humes in Lancaster also.
I recently found a Slaymaker family history book from 1970's that barely references Humes but offered a lot of perspective on the Slaymakers as one of the first families in the area dating back to 1710 land grants with Mary Feree. There is also a reference to a James Hamilton in that book married to a Margaret Boyd, but I can't tell where that fits. I believe there was a later James Hamilton that was likely a sibling of the Hamilton girls the Humes brothers married and that this may be the one that shows up in business relationships with James Humes.
The mother of Elizabeth Humes (m. to James Hamilton) is cited as Mary Miller in records I have but I can't find any source to verify this and also can't place the Miller family this would be related to. There are some sources citing James Hamilton's father as James Hamilton married to Mary Miranda but Isaac Miranda's will offered property to Hamilton but she married someone else. I am fairly sure a will cites out James Hamilton as brother of a Hance Hamilton. One thing that is interesting is that Miranda was an early indian trader and I've seen some suggestions two generations of James Hamiltons also were, and somewhere once saw refernces suggesting that James Humes had been a merchant associated with Hamilton's trading.
There was a Hance Hamilton that was involved in the French & Indian War and I think also was the same or related to one that later ran for mayor of Lancaster. I found some references to an Adams County Hamilton family where an elder Hance brought his nephew James over. There's also a Hamilton line that ends up in Waynesburg PA and a library there is named after one and is said to have some good records that could help clarify things. These may all be related.
There's also an easly James Hamilton who was son of Andrew, both early politicians in early PA. They owned much land all over the place including land that Lancaster was founded on, and the land Independence Hall in Phila was built on. But they are also said to have taken the name Hamilton, and that James supposedly never married. Thatdoes appear to be the James Hamilton that gave the land that the Trinity Lutheran Church James Humes and his brother married the two Hamilton sisters at, but I think that's a coincidence. As to why the generally Presbyterian Humeses would have married there is confusing and implies a possible german Hamilton line, and it's possible Mary Miller's line could be german too. But I don't think that's the case, and it wasn't terribly uncommon for scots to marry at the Lutheran churches. It just seems odd.
Hamilton Humes in Bellefonte was associated with the banking there, and was son of James Humes and Elizabeth Hamilton. Hamilton's wife Ann Almira Bailey was related to Rachel Bailey who was 2nd wife of Edward Crouch of Paxtang PA. Hamilton Humes named his son Edward Crouch Humes and one daughter Rachel Bailey Humes after their uncle and aunt. Edward Crouch Humes was associated with banking in Bellefonte also, and helped build much of the town.
Rachel Bailey Humes married Samuel Humes of a different Humes line in Jersey Shore PA, Lycoming County. That line also founded a bank there, and was rooted in a Robt Hume(s) line that had settled on the Susquehanna and attended Old Hanover Presbyterian Church. They are believed to be cousins of the three brothers Humes but the relationship is not clear. That Robert Hume line begat John who migrated up the river to Milton, but was buried at Old Hanover after he died. I have found the cemetery but not the graves. Samuel from a later generation migrated further up the river to Jersey Shore and founded the bank there, very likely with help from the Bellefonte Humes line.