The seller, on the second counter offer, now wants to sell as-is as he doesn't want to fix anything. 

Once you have a property under contract, you can walk the property(if you haven't' already and even if you have you should walk it again with the seller) and point out the flaws and make a counter offer.

That is when you really run your numbers.If the deal doesn't box, then make a counter-offer at a lower price and explain why. 

Had a counter offer from HUD but I didn't act on it because the price was still too high for me.  

If he counter offers really low, like 2k, I will just thank him and say I will consider it, but after I talk to some other investors and if they dont offer me more.

I found an agent that I could pay a fixed dollar amount per offer/counter offer he writes up and then an hourly rate for misc. things he does "behind the scenes" (which in reality isn't much).  

They are motivated seller's and accepted my counter-offer of a $7500 credit, so I'd call it a win-win!

All that said this will be my first multi (assuming I move forward and we agree on a counter offer post inspection) and I'm really scared.

Multuple offer counteroffers don't have to be for a higher price, you as a flipper/seller, or as a listing agent, can ask them to get preapproved for conventional financing. 

I'm preparing to make an offer on a house. I plan to offer 10% less than my maximum offer. Hypothetically if you made an offer on a house and they countered with your maximum would you accept it or would accept it or ...