I was employed for 8 months and was promised increase after 3 months. I was underpaid for all the employment time & fired

What do you mean you were "underpaid"? And the harassment would have to be very extreme and outrageous and based on you being in a protected class...

Does landlord need to provide central heater for the business property by law?

No, there is no such requirement for a commercial property. It depends on what is stated in your lease. Take a look at that or have an attorney...

I'm going to file a suit against someone who sold me a broken down car and I want to know what happens if he refused to pay?

You can have an attorney write a demand letter or sue the person in court.

In a vacation rental scenario, is it legal to charge guest’s credit card in excess of the security deposit, without his consent.

See my previous answer to your question. Contact your cc company.

Can I sue LLC managers for taking advantage of a conflict of interest?

Yes, but you should consult with a business attorney in order to get proper advise.

My husban is being sued by a lady he hit with his car obviously she wants money how can i win these case n not pay .

Let your husband's insurance handle it.

Can I claim paid rent when the living conditions were uninhabitable?

You can have an attorney write a demand letter or sue in small claims court.

In a vacation rental scenario, is it legal to charge guest’s credit card in excess to the security deposit, without his consent.

Dispute the charge with your credit card company.

No. But the plaintiff can amend the original complaint to add in additional causes of action or facts.

Can the defendant file counter suit in superior court after I filed my case in the small claims court for bodily injuries?

Yes