We can refer here to the music of bagpipes (wind sounds), Ravi Shankar (string sounds), and the historical works of La Monte Young (‘Trio for Strings’) who is one of Eno's references.
-- Sweelinck
I used to listen a lot of Ravi Shankar and never thought of it as drone music, but I guess you're right and it sometimes get's into drone territory, I'll check out his works again, I enjoyed them a lot at the time. Right now I'm listening to La Monte Young and it sounds superb, thanks for the reference! I've never heard of him before.
The E352 Cloud Terrarium seems to be popular for drones, I have seen it mentioned several times in that context. What is it that makes it so good for drones? I'll try out Lugia's tips, a couple of VCOs and an LFO sounds easy enough, I'll see what I can get out of it.