How odd... I think I've dated myself as well.
*Old feeble voice here* When I was a kid, we learned how to type on the typewriters... and we liked it! There were no fancy-dancy keyboards that would erase... we had no backspace key... we had to type every single word correctly or we had to write the entire paper over... but that was the way it was, and we liked it! Sometimes we could use correction tape, but most of the time you couldn't line the word up right, and so you had half of the letter erased, and the other half was still there... but we liked it! And the typewriters made God-awful noises so when everyone in a room was using them at once it sounded like a 747 taking off while dragging a piece of sheet metal behind it... but that was the way it was, and we liked it! The keys would sometimes get stuck on the typewriter, especially if you typed too quickly, but that was OK because most of us had carpal tunnel syndrome anyway because ergonomic wasn't even a word back then, so we just dealt with the pain and typed slower... but that was the way it was and we LIKED IT! *Old voice off*
I was definitely taught two spaces after a period... always have used this and most likely always will... it's just ingrained into me now. *shrugs* Of course, I was taught with them ol' typewriters... (we had an electric one when I was growing up... we were so COOL to have an ELECTRIC typewriter!!!
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As far as line spacing, please, please, please use double spaces on any essay- my students tried to turn in a single-spaced paper once... I handed it back in and said, "I'm old and I refuse to wear glasses. Make it better." It's just easier to read, overall.
Or... something like Encyclopedia Britannica. Or the Modern Language Association. Or... you know. Some huge publisher. Given that I've never heard of webword, I'm inclined to question its authority until I've seen it reviewed elsewhere...
In this case, I wrote 'fairly definitive', because the contents of the article are well illustrated, relatively well supported - and factual within my scope of knowledge. I simply used it to say much what I would say after a fair stint in publishing, because, well, I'm too lazy to type that junk myself... single spaced or otherwise. 
I practically break my neck on the keyboard because double spacing has been hardwired into my fingers for pretty close to 30 years. (Borrowing Hanaeleh's "old voice")
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by researching things to DEATH and creating a library of about a thousand typefaces. Lord it was annoying 