The easiest way to do the caching is to use Cache::FastMmap. It's very fast and you can set the timeout to be whatever you like.
Caching isn't very useful if the requests vary widely, i.e. if people don't tend to request the same page again within your timeout period. In that case, you really would want to run these requests in parallel. Parallel::ForkManager probably is the easiest way to do this, but forking a hundred processes may hurt a bit. The non-blocking I/O approach is more complicated but easier on your system. That's what LWP::Parallel does. There are other implementations, like HTTP::Async. All of them are more complicated than vanilla LWP, and I think that's unavoidable.