1. You need a server side script for leaving comments. You should be able to find one on the internet somewhere; most of them should be pretty easy to use. If not I have a rough one that I wrote and could give you if you really wanted it.
2. To include an RSS feed from another site into your site you will need another server side script to access the file and interpret it. Again, google it and you shouldn't have any trouble finding one that isn't too hard to use. You will set it up to read the feed directly from the main RSS file, so saving one won't be necessary and is a bad idea since it will allow it to become out of date. However, filtering for headlines is very limited and can only be done by very specific methods, like a headline containing the string "heart". Plus you might need to do a little bit of custom scripting to do this.