I can only guess at requirements, and you’ll have other questions I won’t be able to answer, but what follows will probably still be of interest to you.
If you want your GPU for faster video rendering, then yes, the Xavier is good with this. However, the GPU is more limited than on a desktop model. In the embedded world the Xavier is king, but in the desktop world, this would be “ok, but not impressive”.
A GPU can also be used for certain compute abilities. Basically, what people are calling “AI”. Training an AI requires a much faster/larger GPU, such as on a high end desktop, but executing a pre-trained AI model runs quite well on an Xavier. Any software designed to use the Xavier for compute would need to be set up specifically for the Xavier.
The architecture on an Xavier is ARMv8-a (“arm64/aarch64”). This differs from a desktop PC, and so programs designed to run on a Linux PC will not work on a Jetson without recompile (the exception being that shell scripts will work without modification).
PCs connect to a GPU via the PCIe hardware. This includes code to detect GPUs and find them and query the GPU for capabilities. Jetsons integrate their GPUs directly to the memory hub and lack the ability to respond to the PCI query methods.
The drivers for the desktop video cards will not run on a Jetson. The architecture is wrong.
Because the drivers on the Jetson are specific to the GPU being directly wired to the memory controller, these drivers cannot function with a PCIe GPU. Thus, you won’t be able to get a PC GPU to work on a Jetson.
Any drivers you might see for arm64 (outside of the software installer for Jetsons) are not for Jetsons, but for some of the compute warehouse style systems. These will not work for PCIe GPUs on Jetsons.
Jetsons are able to display to both an HDMI port and a DisplayPort. I don’t know for certain, but I highly doubt a third monitor would be possible with default hardware.
A Jetson’s GPU cannot be simply plugged in to a laptop or PC the way an external GPU can be.
These days a lot of laptops can be purchased with a GPU.
In the case of a highly capable and cost effective GPU for display to three monitors, you might consider one of the series of the 1060, 2060, or 3060 GPUs, although you might have trouble finding the right GPU available. Before picking any card though you should be able to give exact details of how the GPU is to be used, and what the requirements are…if it is just a low latency 3 monitor screen, then you could go by “gaming” standards since gaming concentrates on this, but if there were some special compute ability being used, there would be other requirements. From what was told there is no way to provide an exact answer.