Architectural decisions: main site, forum, blog

[Carlcox89]

I've been consulted with on the setup of a project and would like to bounce my ideas off of someone for extra opinions. The main part of this website is very complex and has very customized functionality, so from what I saw it's more of a webapp. However a blog is needed and also a forum is needed. This is the general overview of this project.Because the main part of the website is more of a webapp, I think this project should be separated into individual pieces taken care of by different frameworks and CMSs so that each component does not limit other components. This is a pretty difficult decision to sell though because no one wants to maintain different frameworks and CMSs unless this is really the right thing to do for them.My logic is that because the main part of the website is really a complex webapp, trying to fit it into a CMS like Drupal or Joolma or whatever is going to increase development time and cost. This part makes sense to be created with a more flexible technology like the Zend Framework or Symfony, basically something that's a framework not a CMS.For the rest of the components, I don't see a point of using a framework since many of them are standard components like a blog and forum. So for the rest of the website, my options are 1) to build everything else needed with a single CMS that I'm familiar with (say Drupal), but since I've already went down the road of dividing the site, I thought option 2) why not divide the site even more and choose the best software for each component. Drupal for example doesn't make a great forum. That's just not where its power lies. It also turns out that the people who will be involved in writing the blogs are mostly not the same people contributing to the forums, so I'm thinking that I shouldn't worry about something like training the same staff on 2 separate software. But I can't make up my mind regarding the maintainability of this website. On one side I think it's going to be more difficult to maintain 3 main different technologies: framework for the app, specialized forum software (suggestions welcome), and specialized blogging software (suggestions welcome), but on the other hand, I think this may actually be a lot easier to maintain because one part of the website can be taken down or changed much more easily without affecting everything else. That's been my general idea, but I worry that it might be hard to sell, because it may look like I'm trying to complicate a project. I do think though that this approach actually simplifies it. So any thoughts on this? Are there issues I'm not fully considering? What architectural decisions would you make similarly or differently if you had the same type of problem?