yes a 3060 12gb is amazing for image gen (12 seconds without upscaling, 712x712)
no, your processor is not important
yes, Stable Diffusion has some one-click install options
yes, you can do on linux or windows, doesn't matter
yes, you will have to learn how to use LoRas and upscalers if you want your images to be good
yes, you can find all checkpoints, LoRas, Wildcard, embeddings and any other crazy thing you want to try on
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yes, you need an account to see NSFW things (and active the option on your account)
yes, the learning curve can be challenging, but nothing crazy (not even close to DAZ)
yes, the site has a limit of 1048x1048 (or something close) so upscaling to 4k don't make much difference
hm.... I think this is the 'basic' I can think of