What started out my journey down this road was having to go to work in Alaska in a town with no movie theater, no bowling alley, nothing but fishing (commercial) and long hours. The town has 1300-1600 people during the off-season and it ballons to well over 4500 during the on-season.
Internet is expensive and spotty at best. So some way to stay out of the bars and drinking my liver to death was the first thought in my mind. As I said, I tried XBMC and other DLNA apps to stream media back and forth and none of them worked worth a darn with the large library I had. A that time I had maybe 600 movies and TV shows combined.
Enter a NAS to get the media off of rather full hard drives on various computers and then I started looking at the apps they had available. My first is about the same unit you have. A 202T. No HDMI out, and the same processor and only 2 bays. Installed Plex and had a lot of issues with AVI's and MKV's I had in my library. But MP4's worked! Ok, started asking questions on Plex's forums, and looking at other options.
The conversion scripts I have will work on a 202 or 204. It's going to take them a while to do each movie, but it WILL work. (3-4 hours to do a 2 hour movie.) But the main advantage is, it's mostly automatic. Move the file into the watched folder, come back the next day and move the converted file into a Plex Library folder. Loss of detail on these converted media files? Absolutely NONE! Same bit rates, better compression, cleaner files and no bloat from subtitles or language tracks I'll never use. Best thing was, it puts the file into the best possible streaming format I could ask for from the start.
If you have a Plex Pass you can make use of the new feature they just introduced called Optimize Media. This feature does the same thing the scripts do, but the end result is the media original has to remain in the folder unless you do a bit of file shuffling, and the quality isn't as good as using the scripts. We're hoping to get that quality issue fixed real soon. I got a Lifetime Pass when they were half the price they are now. They marked it up a few months after I got mine. Even at the current $150 price tag, the features in my mind make the costs worthwhile, but what do I know about your situation...
Doing as you suggest, with a "landing" and "download" page is going to put you on some tricky legal ground. You are distributing media you don't own the license to distribute. Even if you weren't officially charged your ISP may shut it down. Streaming the media has already been determined to be perfectly legal if you own an original hard copy of the media. (DVD or BD for example) Since your ISP can't confirm the actual physical possession of the hard media, they have no legal grounds for limiting your streaming abilities. They could still shut you down, but they are on much less firm ground doing so.
Plex already can put a lot of the info you suggested into your library as a part of how it does it's business. The IMDB links are not present, unless you run a browser extension called Transmogrify, but the rest of it is there.
Asustor's hardware is drastically limited by the software. Until they stop breaking things with every update, the hardware isn't going to be as good as it could be. You can't get to the hardware without the software working right.
I have a very well curated collection. Plex makes that collection available to my friends and family, that otherwise they would never be able to use, because a lot of them barely understand what a thumb drive is, or how to download from a link... Install a client app on a Roku, Android or iOS tablet and suddenly they are watching things left and right. What a world of difference setting this up makes for the computer challenged.