No offense, but after trying Plex myself a couple of months ago -- it **bleep**.
If your problem is Metadata then you need to be meticulous on how you name your movies and TV shows. The scraper source used on the Hub is so-so and I don't personally use it.
I would advise you to try WDTVHubGen and the TVDB XML Fetcher .. both are stickied on the general forum. They are fairly simple to use and you have more flexibility with picking things such as your cover art.
You will also find out why the Hub may be failing to get the Metadata automatically. It doesnt give you any real detail on a failed search other than missing information and keying in the name of a movie or show using the remote is a exercise in futility.
Plex is an on the fly transcoder and not a very good one at that. However, it does have more options for metadata. These are two completely different types of media players. With the Hub there is no real point in using Plex at all. Plex does not support anywhere near the amount of media formats as the Hub.
Moviesheets/linksheets and the like are for advanced users - I would recommend getting used to the 2 programs I listed above first before attempting to mess with that.
When you outgrow the Hub you'll probably want to look into a HTPC running XBMC or something similar.