Well, you can use the $1,299 TB3 5K monitor but you don’t need that. You can ge a larger 4K monitor for less. You have many, many choices.
Apple Support has bulletins on all the monitor possibilities for the 2018 Mini. Read them and follow the links. Soon you’ll be as much an expert as anyone here; with that knowledge, you’ll make e right decision for you.
This is important because we aren’t you. I’m looking at the Mini also along with the iMac Pro and the i9 iMac. I need 3 monitors so, for me, using an eGPU is not an option.
A new Mac, set up the way I want with minimum 32G RAM, 580 GPU/eGPU, 2TB NVMe SSD on board, 5K monitor, trackpad, TB3 and AppleCare:
New iMac: 8 core i9 — $4,203 incl 32G 3rd party RAM (total RAM is 36G or 40G depending on 2G or 4G sticks in the base model)
Refurb iMac Pro 2TB: 8 Core i7 — $5,172 includes Vega 56 GPU in base model
2018 Mini: 6 core i7 — $4,096 (incl Blackmagic 580). $3,495 with a 4K central monitor instead of 5K.
This does not count the $$$ for two external/additional monitors (I already own them) nor adapters/connectors which will depend on what I buy.
The point is not that you need a system like mine but that, no matter what anyone says here, myself included, you’ll need to roll up your sleeves and do your own research. Otherwise, whatever you buy become a money pit as you find that you have to add this... then that... and... to get the system that does everything you want.