I suggest you might want to consider making your own emulsion. Go to Denise Ross' "The Light Farm" - http://www.thelightfarm.com/ and check it out.
I've held prints that were made on hand-made emulsion and hand coated on to paper by Denise, and the coating and print quality were so good that I would have had trouble believing it was hand it I did not see the coating artifacts on the edge of the print. (Keep in mind you can trim the edges, and then no one would know you made it yourself!)
Denise has a lot of info there on her site, and if you have further questions this forum can certainly help get you going.
From all your questions, the answers are:
#1 - Yes, you could replace commercial papers. Keep in mind that the larger the coating the harder it is to make. 8x10 paper could be done without too much effort. 11x14 get a bit trickier, and larger, well, you probably need some fancy machinery to do that well. So it you are content with 8x10...
#2 - Speed can be as fast as commercial papers or very nearly so without too much effort.
#3 - Paper does a pretty good job of taking emulsions. If you are coating onto glass or acetate/mylar, then it's another story.
#4 - Hand made emulsions can be tailor made to the contrast range you want to make. Commercial emulsions the contrast range is pretty much fixed. Sharpness is not going to be an issue as papers have lots of resolution to spare.
Check out Denise's site as she has found many economical tools and setups to help making your own emulsion less expensive than buying a full lab of equipment.