Writing a Forum in Flash

Forgive me for posting this same topic in several categories, but I am not quite sure where it will get the most attention.

I am in the process of writing a forum (or at least a forum client) in Flash.

However, many things concern me.

Security
Since there are several SWF decompilers out there, I am worried about hackers. By decompiling the client, would they be able to make modifications to the database, spam, or hack accounts?
What would be some good ways to stop malicious individuals, or at least prevent them from doing any major damage or getting their hands on private information?

I could easily enhance my knowledge in Java, PHP, or ASP.net in case it would help.

Hosting
Most likely, the database will be MySQL or MS SQL. Also, the hosting would need to be able to handle hundreds of hits per day. Also, if any other programming languages are used for the server, they would need to be supported too.

On top of all of this, I have a limited income, which could be solved by advertising or sponsorships.

I would definitely be able to set up my own server, however, I don’t know how much my DSL connection can handle in case the traffic gets to be too much.

Advertising/Sponsorships
Since forums often get at least hundreds of views per day, that would be an ideal market for advertising. Sadly, MochiAds only puts advertisements in games.

Are there any advertisers out there that would be willing to place advertisements in the Flash forum?
Or perhaps someone would be willing to sponsor the whole arrangement?
Where would I be able to get into contact with potential advertisers or sponsors?

I do not need any help as of now for programming in ActionScript, however, if anyone can help me on these topics ASAP.

Andreas