Apologies for not replying sooner. I can't give you a ballpark figure, partly because I'm too lazy to do so. But I've been writing since ... well, forever. Both personally and professionally. Do that regularly, and even in small amounts, and the number of words and pages and files adds up.
I don't know. All of those sites seem to be small, personal passion projects. I'm sure that more than a few people with personal blogs submit to all of them
No. For me, work pays my bills and funds my (modest) lifestyle. With $10 million in the bank (or invested wisely), I won't need to work. I could continue to live my life the way I do and not have to worry about the ridiculousness of the corporate world.