hiya....
ok, first, old addresses wont hurt your score, but you may wish to delete them. its up to you, if you want to try to delete them, dispute them with the credit bureaus. Any dispute with the credit bureaus can take 30 days(45 days if you dispute the items online--better off sending them a letter in the mail anyways for several reasons.)
The inquiries are a different story--they affect your credit score for two years, I believe it is. but there are two kinds of inquiries--those that are disclosed, and those that only you can see. the ones that only you can see do not affect your score at all. its the other ones that you need to look at--and I would not be worried at all here unless you have a lot of inquiries in a short amount of time. That looks to a potential lender like you are applying for credit all over the place and it looks bad. so, if youre going to be trying to get a mortgage, its a good idea to not try to get any other kind of credit at the same time.
About your accounts--you can dispute them with the credit bureaus, and explain that they are duplicate entries on the same debt. They are not required to remove any of them, but I have never done that and had the credit bureau leave them all on my report. For some reason, they always removed the duplicates when i disputed them.
about the co-signed home, I dont think it will be that much of a factor because you are listed as a co-signer and not a co-buyer. If you were a co-buyer, that would mean that you are on the mortgage as a buyer of the house. There is a difference in the way it is reported, and the lenders will know that you are a co-signer and not a co-buyer. also, since it is not delinquent at all, that certainly wont hurt you. But, it may come into play with lenders that have really tightened up their requirements for loans due to the economy--they may consider the house as a potential financial obligation and in that light it may affect your debt-income ratio. I am not a mortgage expert, for that you should speak to someone who handles financing and see what they say about it.