Just replaced engine...still overheating, coolant smell

Hi all, first time poster here. I bought a 2011 Prius off of Craigslist a few weeks ago, and immediately took it in to have the engine replaced with a Gen 4 engine due to a blown head gasket. Carfax says the car has 170k+ miles, but the odometer was rolled back by some previous owner to 120k. After the engine replacement all of the Prius's codes cleared up except for one permanent code, P0A80 "replace battery pack". I'm hoping that that code is leftover from before the engine replacement and will clear with enough drive cycles. I've been averaging 51 mpg on highway and mountain roads and it seems unlikely that the mpg would be this good if the battery were failing. I can also drive in EV mode for about a mile or maybe a bit more, and it maxes out and switches back to hybrid mode if I go above 26mph.
A few days ago when driving up a fairly step hill on the highway, the overheating light came on. I pulled over and checked the engine coolant and it looked slightly low. My friend thought they noticed some liquid under the coolant reservoir but they filled the coolant and spilled some some before I had a chance to look. The light hasn't come on again, but it seems that the engine coolant level has been dropping slightly with every drive (maybe, it's hard to tell). I've been smelling coolant pretty regularly when the AC is on in the two weeks since I got the engine replaced. It seems that the most likely scenario given the liquid below the reservoir is a leak from the reservoir, but when I open the hood the smell of coolant is strongest over on the right side of the engine by the driver's side. The inverter coolant level has not dropped at all. I don't know much about cars, so was hoping to get some ideas from you all about what it could be before going into the shop. I have a (non-dealership) appointment tomorrow but they charge $200 for the diagnostic so I'm hoping to have a good idea of what to ask them to check. They aren't a Toyota specialist as there isn't one near me. A few questions I have:
1. Would the P0A80 would be a pending rather than permanent code if there were a current problem with the battery--does the fact that there's only a permanent code mean it's leftover from before?
2. Could the overheating light be due to the battery being bad and therefore more strain being put on the engine?
3. Are there any common culprits for coolant leaks in 3rd gen Priuses (aside from head gasket)? For instance are reservoir or radiator leaks more common than hose leaks and how should I diagnose if there aren't visible leaks?

Thank you all!

 

Thanks @Mendel Leisk, I've been reading PriusChat threads for a couple months before buying my Prius so having you comment on my post feels a bit like a celebrity encounter!
The engine swap was done by Hybrid 911 in LA. The engine came with a 3 year warranty and when I called today they offered to check the coolant system and bleed it under warranty, so hopefully that will do the trick. I had a pressure test done today and there were no leaks found in the coolant system, so maybe it was an air bubble.
Thanks, I'll check out that saga. Who needs Netflix when one has the excitement of a malfunctioning Prius

 

I was hoping more for a Dr. Faustus than Frankenstein; swapping out its soul for 24 years of incredible power and mpgs...