Hello there , I have question about getting USA GREEN CARD with employer in USA.Can i come on Tourist visa and hire a lawyer ?

That's exactly what you should do. Come to the US, consult with an attorney to find out what options you have to immigrate to the US.

Is there a way my boyfriend (and father of my child) could adjust his status in the US without us getting married?

There might be a possibility, but you would need to consult with an immigration attorney in person so s/he can ask a lot of questions and figure...

Can one apply for residency while on G4 or H1B visa? What are the differences when applying if one holds either one of them?

Much more information is needed. What is the residency based on? Marriage? Employment? EB-5?

Once my fiancee receives her K-1 F. visa and affidavit of support is verified.Will her visa still work if I lose/quit my job?

Once she arrives, you'll still need to file the I-485 and I-864 after your marriage. The I-864 requires that you provide proof of current...

Allowed to change jobs while waiting for I485/I130 approval

Yes. You're fine.

One of the requirements for naturalization is that you spend at least half of the last five years in the US. The re-entry permit does not alleviate...

Can I leave the country for a few years without losing my green card?

See an attorney about doing a re-entry permit before you leave. That could allow you live outside the US for 1-2 years without having to return...

H1b

You can file for adjustment of status after your marriage. When you file, you should file for a work authorization, which should take about 10...

As long as your green card is ultimately approved, you don't need to stay in school under the F-1. If your green card is ultimately denied, you...

Immigration attorney.

More information is needed. What was the crime? You need an immigration attorney to assess whether the conviction qualifies as an aggravated felony.