Didn't check the boards at all today so I'll try to catch up a little.
First, the restriction on 1080p via wifi isn't hard and fast, but some of you are talking about something completely different. Streaming 1080p from Netflix, for example, is not the same thing as streaming a 1080p bluray rip. And one 1080p rip isn't the same as another. I can download a 1080p version of a movie that is 5GB, or one that is 20GB. It all depends on the bitrate and encoding (and other shit, but not important). Netflix is obviously encoded to maximize streaming capability, so it takes much less bandwidth. If you try to stream that 20GB rip over your wifi though, you're probably fucked unless it gets transcoded to a lower quality. And Araysar was specifically asking about streaming his local content, which could be in any format or bitrate. That's why I said "720p only" when referring to him using wifi. He *can* stream some 1080p local content, but it isn't going to be reliable unless he has some next gen wifi router that I'm guessing none of us have. And I'm fairly sure he knows how to get Netflix no problem, so I ignored that end of things.
Anyway, to clarify the whole PLEX thing, you need to download Plex Media Server and install it on your computer. You'll also need to create an account on their website I believe, but it is free and easy. Don't worry about paying for the upgraded membership, you don't need it. Once you've installed it, like others have said you basically point it to your media files and it will scrape all the content. It is pretty damn good without renaming stuff, so I wouldn't worry about it much unless you notice a big problem. Scraping can take awhile at first.
(Note: I've never actually set up my PLEX to work with Chromecast, so hopefully if I fuck up some directions someone will point it out before I screw anyone up too badly.)
Once you've done that, you'll need to get the PLEX app on your phone or tablet. It costs $5. Once you enter your account information, you can now watch anything you've pointed your Plex Media Server to on your mobile device. Combine that with the Chromecast (I haven't done it, so unsure of the exact procedure, but I'm sure someone else can fill in the blanks), and now you're watching your movies on your TV, and controlling it with your mobile device.
You need to keep Plex Media Server running in order to watch, obviously, but the added advantage is that now ANYWHERE you are with a decent wifi/4G connection, you can actually watch all of your movies on your phone/tablet if your PMS is running at home. And if a friend has a Chromecast, you could watch it on their TV as well.
Setting up PLEX isn't difficult, but can be a little confusing, which is why I said feel free to ask. You have to set stuff like what bitrate it will output, and if you do that too high it won't stream right, or too low and it will look bad, etc. That's typically where you're going to set it to 720p, so that no matter what quality your downloads are, it will output it at a rate your wifi can handle.
As an aside, I used to do exactly like you did, just watch right off of my torrent download directory. Nothing wrong with doing it that way at all. However, if you or anyone else ever feels the need to "organize" your files, try a program called tinyMediaManager. It is totally free, no trial version then pay bullshit. It works awesomely, and if you configure it right you can literally just hit a button and it will rename all the files you tell it to according to your settings. It will also auto-download whatever you want it to, like box art or wallpaper art, and even create an .nfo file specifically designed to work with Plex or XBMC, so that when it scrapes it sees that .nfo file and doesn't waste a lot of time trying to figure out if Castle is the one from 20 years ago or Castle (2009), for example. Chaos would have benefited from this program, which is why it occurred to me to mention it now. It has saved me tons and tons of time, but like all programs of this nature, it takes some time to get used to, and don't practice on your actual library until you're sure you know what you're doing. I like the program so much that I donated anyway, mostly because the other one I was using demanded that I pay or lose a lot of functionality after the trial period. Funny how that works. I paid the free program as much as the pay program wanted, simply because they gave me the choice.
I hope this helps Araysar (and anyone else). I know that when I was first getting into this way of thinking, half these terms meant nothing to me, so all the suggestions people gave might have been exactly what I needed, but I didn't know enough about it to even recognize that fact. Keep asking, I know I did, because it is definitely worth it and you'll love it once you've got it set up the way you want it.