1GB internet on a mobile phone?

I am going to buy a new phone but I was wondering if 1GB internet per month is good enough?

I would mainly use the phone to download apps, such as msn/ebuddy, facebook chat, and maybe a game like angry birds (woo) and sky sports news. Is the amount of internet enough?

Also once I have downloaded the app, when I use it does it add to the 1GB of internet allowence per month?

Lastly when I am in the next month of my contract (so back to 1GB) will I actually be able to download for instance 900mb worth of apps again, or will the previous apps still add to the 1GB I get and if I connect the phone to WIFI does it count towards the 1GB?

Thanks for the help. Please give a detailed answer and add any details about internet on a mobile phone that I may need to know about. Of course points for the best answer.