The login bit is of course entirely possible. How you control the login and what they can do thereafter is another matter.

If you are going to have a 'membership' database, you will need to know something about mysql.

You are going to be controlling things using php so you will need to know about sessions and cookies.

I think you should do some reading in these areas and then ask specific questions as required.

You can only legally obtain the data from another web site if they choose to make it available by some means such as an RSS feed. You will have to look at the information and sites you want to get it from to see if this is available. You can always email the webmaster and ask.