use hermes cfw.
no you wont lose games you already have.
use filezilla, thats what ive been using.
not sure why big files are failing for you, you hav e enough space on ur internal hdd right? im guessing youve upgraded cuz 20gig is extremely small for what ur trying to do. you will run outta space quick.
finally, read a little more before you post. the answers are really simple around here even for guys like me. ive had to ask hardly any questions in the last couple months, i simply searched.
edit: forgot to address LB2 and GT5, you will need modded eboot.bins for both of those on hermes 3.41(or for ofw 3.41 for that matter) they can be found in game backups section of the forum under eboot repository. hope ive helped
PS3: 80g BC CECHE01 on Hermes 3.41CFW
2009 Black on Black ZX10r My baby lol