What are your recommendations for a computer specs to run about 100 monitors or maybe even more?
These will be run local not cloud for the fast speed monitoring of like 20seconds or so.
Or do you recommend multiple computers
There is no definite way to arrive at a spec. There are multiple variables that can affect the requirements. The most important of them is how light or heavy the page are. Start by adding fewer monitors and start adding more gradually to see how they work. Adding another PC is recommended if existing one is not sufficient as an incremental way to grow.
Note that if the pages being monitored are from the same website. it can generate a high load on website service content. In this case, one should be polite and not monitor all pages at high frequency. This is not a concern if most of the pages belong are from different websites.