x16 5MP Cams - i7-4790 Good Enough

I think you will not have a good time with those cameras and that CPU. It won't leave you much room for anything

I'd grab something like an i7 8700 for those
 
I cant speak for whether it will be sufficient but if you decide you want more power building might not be a bad option. I was looking at the optiplexes and elitedesks recommended here and at ~$200 for the 4790/i5-6500 they are a good deal but if you are wanting to step up to a 6700 or 8500 you are looking at spending over $300 on a used workstation at current ebay prices. I was looking at doing that but for $400 before tax ($60 or which was a nvme ssd) I've got the components for a SFF ITX build with a i5-10400 which gives me a lot more processing power and a lot more modularity and room for more storage. I went used on the ram and psu but everything else was new.
I have purchased many i5-8500 systems for 300 on ebay. The OS, unless you steal it is 150.