The social security benefits you receive are based on your past earnings. Your SSDI benefit will be the same as your SS benefit at retirement age. I don't believe that an SSDI benefit is based on what your spouse makes. My wife was still employed and I received the maximum SSDI benefit even though I was only 63 at the time. Retirement age for me is 66 in another year.
Here is a link that might explain it. I would suggest you call the SSDI number. They have actually been very helpful when I have called and cleared up questions that I had. Call mid week and you will have a better chance of getting through quicker.
http://www.ssa.gov/pubs/10029.html#part1
Once you are approved I believe that the law says you must get your first payment within 60 days.
Getting approval is getting tougher now as I have heard there is a backlog of 3/4 million applicants waiting for a hearing with an ALJ. Apparently, more are applying and SS does not have the funds to hire enough ALJs. Some states are worse than others.
When I applied for the 3rd time in Sep 2006 using a SSDI lawyer the judge read my application and approved it within 2 weeks without a hearing. I was surprised but elated. I got my retroactive pay within 30 days and everything has been smooth since then. My attorney said that if your case is very strong some of the judges will just approve it and move on to the next due to the backlog. If your case is questionable or the paperwork has not been filled out in a favorable way (that includes doctors letters) a case just has to wait until a judge is available.
The system is really broken and focuses on finding ways to deny the first and second applications unless you have something termainal like ALS or stage 4 cancer. The denial percentages are about 65% on 1st application and 85-90% on the 2nd. The approval rate on the 3rd application when it goes before an ALJ is about 65%. I guess they figure that making the process difficult and denying almost everyone will weed out the slackers and leave only the deserving. Problem is that it penalizes patient who really need the income and do not need the stress of dealing with SSDI.
Hopefully, you have a good attorney. Most who specialize will not take a contingency case unless they feel it is winnable.
By the way, the stats I quoted came directly from an exec with SS who is a good friend of a friend. Those were national ones and since the states do all the approval work it varies from state to state.
Good luck,
Bill