1) A week for each module sounds too short. It might be enough time for a simple module like advertisements, but I think most modules will take longer.
The new user registration code needs some work. You probably don't want to ask for a mailing address. Lots of users don't want to give you an address, and you don't need it anyway (probably). I would like to merge the code for new user registration and Forum registration. There should only be 1 place for users to manage their "account" information. I'd have to think about the SQL tables for these 2 registration areas - I don't like 2 sets of user info for each user.
The File Manager doesn't need much work - I suggest adding Forms authorization to all of it's pages, but that might be all you need to do.
The News module isn't too hard to understand. I think it would be cool to add RSS (Really Simple Syndication) to this, but it's not needed. You can "syndicate" your news areas by providing people an RSS "feed". If you don't know anything about RSS, you do do some web searches on this. You might want to look at the free SharpReader news program (this is called a News Aggragator). This just shows you the latest news from many sites in one place. RSSBandit is another news aggregator lots of people like.
The Newsletter module probably isn't needed. If you do want it, you can work on it later - it doesn't have to work on the first day.
The Forums module is the most complex and this will take time to modify. I'd say you should remove the focus on email addresses (because of SPAM), and make a way for people to upload an avatar image. The image could be stored as a blob in the user table. You'd have to check the size of the image and make sure it's small. But, the easiest modification is just to remove avatar support - it's just a cool feature, and not really needed.
You should also read my ideas here:
I might estimate 2 months for the whole thing, and that doesn't count the time to customize it to add other things, or maybe a new graphic design (which is not my strong suit!). Of course, if you've worked on a lot of web sites before, it might go much quicker than this.
2) You need to understand the nature of a virus. If you get a virus on your system, it will normally affect programs on all your drives - depending on which virus it is. I had a nasty one last year, and I had to reformat all my drives and reload windows. I'm much more careful now about downloading and running programs, and I use both ZoneAlarm v4 (firewall software) and Norton Antivirus. Be careful about trying ZoneAlarm 5 - the first relase of v5 was not compatible with ASP.NET - it caused me a lot of trouble! Of course, a hardware firewall is your best bet if you have a high speed internet connection.