recovery does not recognise / mount SD card
Well, that one is solved!

The problem was not the SD cards, but the fact that rooting etc. the Desire caused it to USB-brick. Never heard that before. Some people can cure that with fastboot commands (did not work for me) but the 4ext recovery provides an USB un-bricking function.

Long story short, I'm running Spezi77's version of LiquidSmooth 3.2 on my Desire now after changing to 4ext! (following the advice on this link)