I actually just got approved for a loan. The guy said they were looking for 625 or better on the credit score and less than 45% debt-to-income. I have two charge-off accounts on my credit. I paid one and am leaving the other.
I did have to provide 3yrs tax returns with W2s, 3 months checking stmts, and a month of pay stubs. They really want a good picture of your finances.
As for getting your credit up you really only have a couple options.
The charged off accounts are about equal on the score, so that is not much help. (they may ask you to pay them in order to approve the loan though)
Get all of your balances down to $0, this will get your utilization ratio down
Then just waiting for accounts to get some age on them (no fast way to do this)
It will take a few months for things to change though. The score is only updated monthly, so any affects could take a while to show up.
If you are trying to cash in on the $8k your window is getting smaller. You have to go under contract by April and close by June.