I signed a contract, and now i want to leave, am i trapped?

One would need to review the contract in fully to properly advise you. This website not designed for that. A full consultation would be...

I would like to know if I could cancel this contract and how

One would need to review the contract in fully to properly advise you. This website not designed for that. A full consultation would be...

Can i serve a 3 day notice for a tenant who has illegally hook up a washer and dryer, or pet in a no pet lease

If the tenant is in violation of the lease, which they are if they have pets, then you can issue a 3 day notice.

What do to when a landlord does not enforce quiet enjoyment.

You can have an attorney write a letter to the LL and/or the violating tenant. A full consultation would be necessary to properly advise you.

If the lease provides for late fees, then yes.

You have may claims for breach of contract, but the agreement would have to be fully reviewed to properly advise you.

Can one get fired on the spot and be told "i'll call you when your final check is ready".

Assuming they are at-will employees, yes.

Does the owner of an LLC have a fiduciary interest or responsibility to the person he has a contractual relationship with?

Generally no, there wouldn't be any fiduciary duties in this situation. However, you may have other claims against the LLC.

Yes, you are legally obligated to pay them back.

In the CA Central District Court, it is clear that the Plaintiff has no case against me due to res judicata in prior suit

You can try to file a motion to dismiss.