Content aggregation website for social media sites

I am looking to build a website that can aggregate content from RSS / Google Alert feed. In addition, I'd like the site to have free form text boxes that where users can type 140 characters. The site should also be able to replace keywords with hashtags. The site should have a built in scheduler (date and time) that users can associate with particular content. The site should be subscription based so will need a database to store usernames / passwords. The site should also fetch content from the RSS / Google feeds every few hours. I'd like a very simple landing page (something like [login to view URL]). Once in the site, I'd like to have a simple dashboard where a user can have the RSS / Google Alerts tab and create subfolders within that tab. There should be another tab that allows users to create an ad hoc number of 140 character set posts. There should be a tab that allows the user to manage all of their hashtags. For example, it should allow a user to type in a keyword and for all the content that the site pulls in from the RSS / Google Alerts or user entered text, the user should be able to select an option to replace any predefined keywords within that text with a hashtag. The site should allow users to export content to a .csv file and allows them to select individual items or all items at once to include in the .csv file. The export function should interact with the scheduler to associate a date / time with the content. The .csv file should export the content in the form of date / time, user defined test, and then any urls associated with that content.