Connecting 3 monitors to macbook pro 2018 via thunderbolt 3

I looked for 20 minutes for a post similar to mines, and couldn't find one. Which is interesting to me, because I don't understand why people want to use the display to HDMI instead of using thunderbolt USB-c port natively instead. Before I get to this...I shall ask my question.

I plan on buying a MacBook Pro-2018 15 inch for my home-based business. I need to connect 3 monitors to this laptop. I understand the 15 inch MacBook Pro comes with 4 thunderbolts 3 ports. I plan to buy 3 24-27 inch monitors that are 4k display. Also, I understand that the charger for this laptop uses a Thunderbolt 3 port, which leaves me with 3 left. Will connecting 3 monitors that have Thunderbolt 3 ports leave me with performance issues? Will the refresh rate lower?

Finally, why do I see a lot of post with people using old 2.0 display port to HDMI; why they can use Thunderbolt 3 port natively?

I currently use 3 4k displays (Dell P2715Q) on a MacBook Pro 15" 2017 (GPU: Radeon Pro 560 4096 MB).

Two monitors are connected to the right side ports/bus and the third one (plus a dock for charging/USB/etc) are connected to left side ports/bus. The monitors are arranged in a "H-shape" with two monitors flipped 90 degrees.

I've had this setup for about 6 months now and while it is usable, I do face some issues from time to time, always after waking up the monitors after sleeping overnight:

1. The orientation (90 degree rotation setting) tends to get messed up in two of the three monitors and I have to waste 1-2 minutes fixing it on System Preferences > Displays. The cause for this likely a software/compatibility issue on macOS and I have had this on a two monitor setup as well.
2. Every now and then the ONE of the monitors connected to the right bus fails and I can't make BOTH work again without a system reboot. By repeatedly disconnecting/reconnecting the mDP cables I can get EITHER of them to work, but often not BOTH simultaneously, which is pretty annoying. I feel like this is a hardware issue, perhaps GPU memory issue, but more likely something to do with the Thunderbolt bus bandwidth as it always happens to the bus that has 2 monitors attached to it and never to the one that has only a single monitor attached to.

TL;DR: It is possible but be prepared for some minor issues and eventual monitor "loss" followed by a system reboot.

For anyone trying to do this using a dock that has multiple display outputs, the MacBook Pro 2018 only has two thunderbolt busses, but 4 ports (2 ports per bus), as a result, if you try to connect three external monitors, you will need to use different sides of the device.

If you try to connect all three monitors into two ports on one side, it won't work.

From the MacBook Pro Technical Specs page:

Simultaneously supports full native resolution on the built-in display at millions of colors and:

Up to two displays with 5120-by-2880 resolution at 60Hz at over a billion colors.

Up to four displays with 4096-by-2304 resolution at 60Hz at over a billion colors.

As per Apple, you should be fine with upto 4 4K display.

Yes, you can connect 3 x 4k-monitors to the 2018 15" MacBook Pro - and yes, you can use USB-C to DisplayPort cables to connect the monitors.

Doing it this way will take up 3 of the 4 ports, leaving one available for charging, as you describe.

You will not suffer from lower refresh rates, nor "performance issues" as such that are specifically related to connecting the 3 displays in this manner.

You'll often see people using docks or other adapters to allow connecting multiple displays to a single Thunderbolt 3 port - leaving more ports available for other things, and simplifying connecting the displays when docking/undocking. In this case, the docks often offer HDMI ports instead of DisplayPort.