I have the same reel and run 50lb braid, as far as amount of backing goes I can't tell you exactly how much but if you have got time the following is the best way I have found. I use 30lb for backing.
Firstly spool your braid onto the reel and make sure you wind it on pretty firmly. Once this is done join your backing on and continue to fill the spool until it is to the desired level and then cut the line. Once again make sure it is pretty firm but probably not as tight as the braid. Now get an old reel and wind back off the backing and then once down to the braid, wind it onto another reel. I sometimes use some of my old alveys to do this.
Now its just wind the lot back on starting with your backing and then the braid. I can't stress enough that it has to go on quite firmly because otherwise over time the braid will settle in and the diameter of your spool of line will decrease and this leads to more winding to retreve line.
Hope it makes sence.
Cheers, Clutter