To everything you asked, it depends. I don't want to say that you shouldn't do it, because emperor Lelouch is amazing and you can do anything you can put your mind to, but it's a big undertaking for a first cosplay. First, can you sew? Because you'll definitely need to know how to sew-- Emp!Lulu isn't something you can put together from a closet cosplay.
As for the shirt, the answer is no, for several reasons. First, Lelouch's collar sticks straight up; unless you pop it and do some funky stuff, it won't look right. Second, his shirt doesn't button up the front like the shirt you bought does. Third, the shirt has ornamentation and trim that needs to be added. There are five buttons on each sleeve, and from what I can see, each sleeve is made from two pieces of fabric, not one. Finally, you'll be very unlikely to find a material that matches in both texture and color to make the rest of the outfit (too many different shades of white!).
As for the more intricate questions, I don't know-- I hope someone gets back to you, because I'm hoping to get an Emperor Lelouch done by the end of July. I'm in the nitpicky research phase right now, so I hope my comments help.
P.S. Some of the reference pictures you use are fan art-- if you want to be accurate, I'd stick to official images. I actually looked up the episodes where Lelouch wore the outfit and am now working on sketching out the specifics of the outfit from each angle so I can get a good idea of what I'm getting myself into.