Mac pro too slow to use, spinning ball, no finder response, only hard power off, installing system stalls at 18 minutes left.

Question

mac pro too slow to use, spinning ball, no finder response, only hard power off, installing system stalls at 18 minutes left.
It is taking an hour to power up and mac apple logo appear onscreen. No finder controls or "clicks" are being recognized. Spinning beachball all the time.
Using hard power off and holding the mouse down, I was able to open the optical drive and then restart with "c" and ask the dvd to reinstall the system, but it has stalled before finishing the installation.
This happened about 4 days ago, first it started responding slowly, and then it just keeps spinning the beachball. I can't find hardware test. I did run etrecheck, it did not have any error messages, but I can't copy or move the data anywhere.... I am not able to access the mac pro with another machine, and now I am stuck in install freeze, so I can't copy etrecheck by hand onto a piece of paper.
Without being able to finish a reinstall, what can I try?
After it got bad, and before it got REALLY bad, I managed to repair permissions, but it took a long time. Most of a day. When I restarted from that, things were only worse.
Mac Pro 1,1 , 11 GB ram, 7300, 5TB hard drives, OS 10.6.8,  the drive containing the system folder is/was 700 used, 290 free. While I could get commands to respond, I put Activity monitor on the desktop and watched it.  System memory was 3.31 GB used, about 7 free, and some wired. No app was using a huge amount.
what should I try next? I put a bid on a new/old machine so that I could move the 4 hard drives over.

Answer 1

Thank you for all your suggestions. Please correct me as I articulate this.
I have three versions( 5, 6, CC) of the Adobe Master Collection which I keep active for different clients. I have final cut and motion. I have Office 365. I have a collection of graphic apps that are individually not too big but in all, my app folder is 65GB and my bootcamp partition is 61GB. I can't fit all this on 120 ssd and a 256 will be full once I install, correct? drives should be half open?
Somehow I did not make it clear enough that I was trying to copy onto a 2TB drive I had just initiallized in order to try and save files from my startup drive. I don't use time machine. I take a day or a few days worth of documents and physically move them to another drive at night.  If a series is finished I make two dvd's as well. The second black drive that was failing was the drive I moved my backup documents onto. At no point was I trying to backup onto the failing drives. I was trying to copy off both of them onto the other two drives, a third aux backup that has been there for a while, and a newish 2 TB which I designated as the startup drive when all this trouble started.
I wondered if there were any good techniques for trying to get the data off the failing drive. Thanks for the suggestion of Data Rescue 3. I don't have it yet, but I will try it as soon as I get it. I was never trying to repair in place.
I am very interested in getting a pci bracket and an ssd, but I may wait until I can afford the larger one. If I get an older bracket that is compatible with my old mac pro 1,1  ,  I'd like to be able to move it to a mac pro 3,1 if I get one. Will the larger ssd drives be compatible with the sata in a pci bracket that can work in my mac pro 1,1 ? sata 2 versus something else? If 240 or 256 is my size limit, how much more than my 65 and 61 GB partitions can I put on there? How much of a scratch disc can I make if I leave another 39 GB of headroom on my bootcamp partition? I'm filling 165 GB without making any allowance for temp files.
You have said that 120 is enough for any system. I think I must be misunderstanding something. Are you saying that assuming that most people run office and photoshop and maybe lightroom?
I have and use 4 HDD in this machine, mostly for document storage in two places.
I took out all but the group of 2GB ram chips I bought a year and a half ago. The old ram had passed the hardware test the last time I had access to the hardware test. Two black drives failed, one was a year old and one was a year and a half old, and that it may have been exacerbated by the heat wave. I don't know why the video and the monitor were affected save that the startup drive was failing. I am trying to replace the card.
With all this said, I am also looking at a used mac pro 3,1 with a better video card since a newer machine will likley be compatible through another OS upgrade. If a machine costs only a little more than a new card, it might be a better way to go.
I don't have any sources that offer an ssd for 100. ( of a size that is useful)
How large is your application folder?