#2. Absolutely correct. Many were Irish immigrants.
Also there were a lot of immigrants from other European countries.
My maternal Grandfathers family emigrated from France in April 1912. He was 8 y/o at the time. They were scheduled to take a connecting steamer from France to Southampton to rendezvous with, as he described it, a great brand new liner making its 1st voyage. They would have been steerage passengers
Their emigration papers weren't in order so they missed their connecting voyage and were delayed a week. The family took the next transatlantic steamer. My Grandfather said he was disappointed that they missed the big new boat. It was the Titanic.
He had a great time as an 8 y/o on the voyage over. He said the Captain even pointed out the iceberg that did the Titanic in. It had a large red streak down its side. But for some clerk in France he and the family would have been on that ship.