Oauth Refresh Token



I am a noobie to oauth. I have watched some videos on authenticating using oauth and have gotten the authentication part going but I have a couple of questions.

Q1- Do access tokens expire?
Q2 -Do I have to make the user go through the whole user authentication process (with user authenticating the app again) once the twitter access token expires?
Q3-Is offline access to user’s content possible once we have the access token

Ok so just to give some more context this is the scenario I have. Basically our mobile app is looking to integrate with twitter and there is a server side to it which needs to munch user’s twitter feeds. And this is how we are thinking of doing it. Once the user aunthenticates our app using the mobile platform, we want to store this user access token in our server, poll his feeds at regular intervals and do some data munching on his feeds. For that we need

-Offline access to user’s data
-Get a new access token without user’s intervention if the previous one expires.

Any response/help towards this would be appreciated