Yes, it's based on the pinwheel in some newspapers - but I haven't said that any particular letter has to be used.
No minimum number, though I expect you all to find patch, work and patchwork. Maximum is however many you can find.
I have a concise OED which is about 20 years old and I will go by that although if you find any modern technological words I will make an effort check them elsewhere. There's slang and slang, some words are in the dictionary, some aren't. There's one which I found which has two altrnative spellings, I will allow both spellings so if you find that one and include both spellings it will count as two words. No foreign words or foreign spellings which aren't in the OED, and no abbrviations.