[drambit]

To start things off, I have a lot of experience repairing electronics in general, I have a very nice Hakko soldering station, and I have repaired headphones quite a few times before, but this time I want to do a high quality job so I have some questions for the DIYers here.
 

1. What cable is actually recommended to do this with? Just from lurking a bit I have read that Mogami makes some reliable stuff, but is a bit of a challenge to find in Canada, and I have also heard of people just buying long auxiliary cables and chopping them up to accomplish a similar thing.
2. How expensive is this kind of thing generally? All I need to do is desolder the old flat cable completely, and replace it with a brand new wire and jack (currently the cable is damaged somewhere so the sound in the left ear does not work.) These are pretty cheap headphones to begin with so my budget is ~$20 CAD.
3. Is the fancy lacing everyone does here to sheath cables actually necessary at all, or is it just cosmetic? I would imagine that the sheathing on the inside of Mogami cables is good enough on its own, I don't actually see what benefit you would get from getting fancy shoelace sheathing other than it basically just looking pretty. 
4. Is it smarter to try and find a flat cable to replace the broken flat cable that is currently in the headphones, or is it smarter to just make slight modifications to the headphones that allow normal cable to come through properly? I would personally imagine the second option is generally easier and more viable, but this is my first time posting around here so I don't really have a good feel for how things are traditionally done with Hi-Fi audio. 
5. How are Y-Junctions made? This particular set of headphones has a wire coming down from both earcups that meets at a junction and then continues down to a singular jack. I have heard interesting tricks like buying a 3.5mm to dual RCA cable and cutting off the RCA ends, or buying a cable that is effectively just two cables stuck side by side, or variations of that. I can't think of a way to do it with normal cable that is both space efficient, attractive, and robust though. The wiring isn't a problem for me just the actual housing and creation. 
6. Is there anything else I should know as someone who has never tried to do a really good job of this before? I.E. good quality jack sources, good cable retailers, maybe interesting tricks or mods, anything like that.

 
Thanks for any assistance, I would like to go a bit above and beyond with this project (within reason of course, they are cheap headphones.)