DocumentalLy is probably the best synthesis of their folk rock meets techno style and I think it’s my favorite of their albums, but their follow-up (and most recent, though still nearly five years old!!) self-titled album is also great. There are amazing selected tracks from their previous albums too (“Ame(B)” and “Aruku Around” are standouts).
Their YouTube videos are blocked in the US for copyright reasons so I don’t know what’s available there, but DocumentaLy has “Bach no Senritsu o Yoru ni Kiita Sei Desu”, “Identity”, and “Endless” while Sakanaction has “Yoru no Odoriko”, “Music” and “Boku to Hana”.
I hope you enjoy them!