I'm very certain that you will be very satisfied with the 902/903 if the tasks you've mentioned above are the main focus of your work.
In the latest version of the RSS reader (firmware 2.0.4 from January) you will get to each article in the feed a clickable link. Once you click that link the webbrowser (called midori) will open that link and you can easily download files from that webbrowser to your reader. So although I haven't explicitly tested this functionality I'm 99.9% sure that it'll work.
Of course I assume that the link to the document in your LAN is done properly with http (or probably ftp) and not samba. Samba (the windows file sharing service) most certainly won't work.
The good news is that no matter if it'll work or not with RSS downloads, a very similar topic has been discussed just a few days ago over at the german forum. And since the interest in this was high I've written a small
script to comfortably download first one file from a known place which contains all the links to the files you want to download. And in the second stage all links from that file will be downloaded. If you have a lot of files this is probably more useful then clicking each file in the RSS feed.
Are those files served from a samba share or are they on http or ftp? I think this is the crucial question you have to look into. If it is anything else than samba, I think you can go and get the new pocketbook. If you want to use my app webdown to use for your setup, I'm certainly willing to assist you configuring it for your needs.