new owner, having starting issues, questions

HI all, I'm new with Prius and I posted previously about maybe same problem, but I'm also now noticing more so I'm posting again with everything I'm experiencing, since it's possible they may be related? Sorry for the long post but I want to be as accurate as possible. Thank you in advance.

I just bought a used 2014 prius v with 18,723 miles and have two main problems the dealership and mechanics there can't seem to figure out. Nothing shows up in diagnostic codes, I've had the connections to the 12v checked, and no one at the dealership seems to know anything, or anything they want to tell me about.

1) Sometimes it starts, and then when I put it in drive or reverse, it shuts down. After several tries it starts and stays on and seems to drive fine. On another occasion the dash lights lit up but it didn't start at all until 3-4 tries. This has happened with either a cold or a warm start. The dealer says that the hybrid battery charge has nothing to do with the engine starting and then shutting down, or not starting at all, but when this happens the hybrid battery shows only 2 bars, even if it was at 7 when I parked it just an hour or two earlier. The 12v was replaced in March.

2) The hybrid battery loses its charge overnight. It can be at 7 bars when I park for the night, and only 2 when I start it the next day. It also seems to fluctuate occasionally while driving. Is this normal?

3) Not sure if this is a problem, or has anything to do with the other issues, but when the ICE starts after I'm moving, it sounds like a revved up mustang firing up. It didn't do that on the test drive so I'm wondering if that's normal or has something to do with the other issues. It also doesn't do it all the time, so I'm not sure if everything is engaging as it normally should. And when driving at a constant speed, it seems to buck somewhat.

The 12v was replaced in March. Looking at service history since 2014, the 12v has been replaced twice (so it had a new 12v when bought in 2014, and 2 new 12v since then, so that's 3 new 12v batteries with only 19,000 miles). The dealership says the former owners didn't drive it enough and now it needs time to catch up. The manager told me I need to take it on a long trip to fix it...WHAT??? In the 18 days I've had it, I've driven it 979 miles.

Am I overthinking things? Any help is appreciated.