I spent some time this weekend trying to get a NetBSD desktop going. It's a muuch heavier lift than OpenBSD -- by orders of magnitude.
The Raspberry Pi Foundation now has a very nice program available to put Raspbian and other OSes on SD cards. https://www.raspberrypi.org/downloads/
I haven't done a NetBSD install in quite a while. I have the image on a USB, so now's the time.