I can't help much on the other questions you have. Someone should be along that can give you answers to the other issues.
As to SSI and SSD, they are different. SSI is for low income disabled people. It's basically government welfare so to speak. A couple can't have more than $940 in income a month. I know this because I tried and hubby makes wayyyyy too much money for me to get it.
SSD is disability. You have to have a certain amount of work credits to qualify in the 10 years prior to applying. I had worked off and on but was short about 8 credits or so. That's means without those credits, I can't get disability. So shoot me for being a mostly stay at home mom all those years! *rolls eyes* Without that, I'm left on my own to pay for everything.
This link answers the question as to how many credits you need in order to get disability.
http://ssa-custhelp.ssa.gov/cgi-bin/...i=&p_topview=1
If you have earned 20 credits in the last 10 years then you're eligible for SSD. I was short 8 credits and one year too old. I was 32 when I was injured and got rsd and I had 12 credits. Had I still been 31 or even 30 in 2003, I had the 12 credits in the time period needed and would've been eligible. Talk about unfair!

Oh well.....life goes on.
I wish you much luck in getting it the first time. There's quite a few people that can give you pointers on what to do so you can up your chances.
Hugs,
Karen