Blue screens, no idea.
Only one GPU being utilized? Well, a single RX 480 should run APB at more than 120fps. ("Should" being a key word, because APB is trash.). That said, you can download a program to monitor your GPU usage, such as MSI Afterburner, then see for yourself how much of your GPU is being used.
If I remember right, I had a 7870 that APB would only use about 70% of. Meaning even that old card wasn't being stressed to run APB at max.
Invisible characters are definitely a thing with Nvidia cards. Not sure about AMD.
You may also run into extremely glowy characters. Or more specifically, a single piece of their outfit.
Apb is 80% cpu intensive
I play at around 113 fps at max. Settings AF, AA off
I5 4690 (4,3ghz OC, 1,200v) around 80% usage
2x gtx 970 around 30% usage on single card
16 gb ram 2666mhz
Game is on SSD which helps a lot to load district after joining and eliminates then random spikes and freezes
Psu: 650w and yes its enough for double gtx 970 + OC on CPU
CPU Cooler: CM Hyper 103
Temp while stresstest: after 4 hours 65°
Temp while apb: up to 45°