As marc2590 mentioned, renting games would be the better option. In regards to opening the contents of the files. As most ps releases are either in rar format and some in 7z. So i'd suggest you get 7zip. Once all files are downloaded, simply extract or join them, Which ever is the case.
I assuming you are downloading from filehosting eg rapidshare etc.. Given the whole all in 1gb parts+ one at a time. As long are so get the downloads it doesnt really matter. when you say "my current speed is about 70KB. per second" is that average speed on a daily basis ? I used to live in shared accomodation and the download speed was abysmall. Only to find out my mates were using newsgroups. NZB totally kills bandwidth, literally!!!
Well everyone has different download speeds, the question is how long are you willing to wait till the download finishes moreover which ps3 games are you downloading. As there are the small sized ones eg Ninja gaiden <5Gb to games like Resistance| god of War 3 > 15 Gb. Personally, I stay away from anything over 15GB. With 15Gb it should take me close to 8hours. I just cant stand waiting too long, besides I hate leaving my backlog of downloads and laptop on too long.
Another program you will need is a good ftp program - use FlashFXP. Simply connect to the Ip as stated from the PS Settings >> System information dash board. I've been using flashfxp since xbox1 hack and it hasnt failed me and very easy to use.