Couple of things to add:
Firstly... see here: #27
For an interesting thread with further info about using FOUR screens at once (2016 MBP 15" + Samsung 1080p TV + 2x LG 5K's) — TL;DR: basically one of the 5K's drops down to 4K and scales up to 5K.
Just for fun I also tried a four screen setup when receiving the LGs and before properly installing them. The setup was 2x LG 5K, 27" Cinema Display (1440p) and the internal display. I verified that both LGs were running in 1440p HiDPI mode, so at 5K. What I noticed was that the sequence in which I attached the displays mattered. Otherwise I couldn't even get all three external displays to show an image.
Man, that must be so frustrating. Well done for your dedication.
The dual monitor setup is so worth it though, the 15" TouchBar with 2x UltraFine screens is easily the best computing setup I've ever had.
I plug in three reversible cables and I get power, 2x 5K screens, and a whole bunch of USB peripherals + Ethernet (admittedly running on a Satechi hub, since the monitor hubs are useless). Plus, I get consistent colour across all three screens (incl laptop) and glorious retina resolution. It's awesome.
Thanks. It was a hassle but worth it! Love the setup as well and it's something I wanted for a long time. Every since getting the first Retina MBP in 2012.
I also use a separate USB hub for the peripherals as the display hubs are not good performers. I even use the old USB 3.0 (type A) hub I had with an Apple USB-C adapter. Works nicely.