re: Where should i have my media server running and which one (plex,XBMC)

I built a separate machine to use as my server (needed that core i7 for transcoding, ya dig?). I also use Plex because it goes from installation to watching movies in roughly no time flat. As for the connection, my server is wired to my router but my clients connect via wifi. Your laptop will be fine for running the server if you maintain a library of files all your clients can play natively. This means finding the list of codecs your tv/ps4/roku/what-have-you can play (they won't list things in the manual if they can't be played natively) to eliminate transcoding.

If you don't keep your media in a format your clients can play natively you'll be transcoding and will need a heftier processor. I'm assuming your laptops are old btw, you can use passmark benchmarks to score your laptops processor to see if it can handle any transcoding at all.