Personally, I would postpone learning about fork and lower level socket programming. They are necessary to learn about but you better learn about them once you have a situation that requires you to instead of learning about them now and never getting to something that produces results.

I would avoid POE and IO::Async for the same reason - unless you have a situation that requires you to use a state machine or callback based approach for concurrency, knowing about them serves little purpose.

If you want to write servers or middleware for SOA (which I presume includes the buzzwords REST or Microservice, nowadays), I would look at Dancer or Mojolicious for getting a quick start. They both can act as stand-alone servers but can both leverage Plack/PSGI to use other webservers. If your application ever outgrows what these frameworks provide, Catalyst gives you an environment that needs far more up-front setup but supposedly provides much more structure. Personally, my applications never reached the complexity that might warrant using Catalyst.