A PC can support up to 127 USB addresses on a single computer in theory, so your hub plan could work. In practice it is not quite that simple. Each USB hub claims some of those USB addresses, so it more realistic to aim to connect up to 50 cameras rather than 100 cameras to a single PC. It is also preferable that each camera is connected to a port that has its own USB controller, rather than sharing the USB controller between more than one port
Again, in practice, although you may be able to physically connect 50 cameras, processing would likely be at a standstill because of the extreme drain on the PC's resources. It is more practical to have maybe 4 cameras at a time active, and turn them on and off in batches of four until all the cameras have taken a snapshot and you are back at the first batch to begin the cycle again.
If compactness is a key need and budget is not a prime concern then the new Intel NUC 8 mini-PC may meet your needs. It has a very small form-factor and multiple individual USB 3.0 ports. The cost would be around $1000 for the basic unit (there is a cheaper model with a lower spec), plus some extra components you need to add yourself such as RAM memory.