Will immigration check my I 9 if I did not disclose employment?

Could, but if you only had to disclose 5 years, that's it.

Getting payment for services?

You should meet with a local attorney, and discuss liens and other methods for getting paid. Having a relationship with a local business attorney...

Do I have to pay it back?

If it is not yours, then it is not yours. Mistakes happen.

I was hired to build a website and I haven't been paid

If you met specs and provided timely service, time to put a demand in writing and/or get legal advice. If under small-claims court dollar amount,...

If I abandon my Green card status, what are the possibilities for me to regain a green card again?

Can't agree more. If you qualify to apply for citizenship, that is the way to best protect yourself. Happy to talk about it if you wish. Good luck.

Can an oral breach of contract occur 24 years later?

You really need to find local counsel to help you. Business litigation attorney would be a good start.

Can I apply for change of status from H-4 to F-1 myself?

Attorney or not ? It's like most things we attempt to do rather than using a professional.... What we don't know is what gets us.

If you have valid papers, your H1B allows you to exit and return during validity. Why enter any discussion ?

I am a u. s. citizen i petitioned for my husband 2008 we recieved a letter of approval from immigration what know.

Is your husband overseas ? and you child ? What country ?

What do I do if I perform a housecleaning service then customer cancells their check?

If you provided the services, I agree you should make a claim. Just filing it will probably cause them to pay up.