#1 5-6GB sounds right
#2 no idea I don't have the epic collection box (not available in Europe)
#3 Login to your master account and there should be an option in there somewhere that let you choose which player you want to give the mask to. The mask can't be traded or sold so choose the char carefully.
8-10 gb is recommended space so that IF the game files fragment a few times, or the game expands again, youll know you have enough space.
afaik theres 3 install disks. might be wrong. never used the disks yet lol.
the in game item comes to you on the Tuesday server maintenance schedule but ONLY when you tell NC what character to give it to,and ONLY once. non transferable means make sure you wisely choose your character.
to choose your character go into your playNC account, click the account details button and at the bottom of the page is "select a character" button.
i suggest trying some characters and when you find the one you love, KEEP it and play it, and THEN give the special item to yourself.
Just one disc, its a DVD. They could have released a CD set for it but I really doubt it. Pretty much everyone with a Lineage2-ready system have a DVD drive.