Hello.

Being a longtime krautrock and drone fan, i fancy the idea of developing a realtime cosmic-meditation-music-machine based on Pd. I don't really know much about Pd, i'm just a beginner and have no problem about starting by using patches other people made. Right now i must confess this is just a fetishist idea based on the image above.

Now seriously:
I owe a mac and no midi interface at all. What hardware do i need to start with?
I suppose i would need loads of knobs and faders. I welcome ideas or pointers, so i can find the right place in the cosmos to begin with.

you don't really need any hardware,if you don't have any.You can use your computer keyboard, you can use a gamepad for PS3 which is really cool, you can use sensors, an electric toothbrush.... Maybe these tutorials could help you. http://www.pd-tutorial.com/english/ch03s02.html (the whole book is awesome).
Another really good book is here: http://dm.ncl.ac.uk/courseblog/files/2011/02/pd_intro.pdf

I do ambient drones with PD and use a lot of sine waves and filtered noise,It's fascinating the amount of great sounds you can get just by using filters and a couple oscillators, you can use Freeverb as a reverb that is really good for drones but something that's really awesome is patches that Tom Erbe from SoundHack released based on his free plugins, you should get those, they're awesome for drones, it's based on spectral synthesis:(soundhack.com/freeware). You can also use VST plugins in PD but you need the Pdvst abstraction.