well, first off, "blogpage.php" has to be called into your theme. If you create that file, it won't instantly use it for a particular page, like "blog". they don't work that way.
Pages can be specified by going into the page.php file and doing something like if(is_page('2')) { stuff here for Page ID 2 } else { format stuff for all other static Pages }
Now, you *can* have a "flow" of posts actually appear on static Pages, but it requires some serious coding to do so. (I'm actually doing this right now for a site I'm working on - been trying to get the code refined for about a month now, and I'm still not finished yet!) Normally, you don't even need to do something like this, as you can accomplish what you're looking for just by using Categories and conditionals. (My case above is something extreme, and I don't recommend doing it at all!)
But if I'm reading your idea correctly, what you're *trying* to do is use WordPress as a CMS, where you:
1) have a static Page as your index page on the site.
2) have other static Pages, to emulate a regular static HTML site (Pages are generally for content that will never change)
3) Have a "blog" section on your site.
4) have a "Portfolio" section, where the "blog" would *link* to the "portfolio" section, but the blog would never display actual portfolio posts. (In essence, you'd have a link to the "portfolio" category, but anytime you posted to that category, the only place you'd see that post is if you were *in& that category - no place else would show it)
You *can* do this.
I'll tackle the "portfolio/blog" stuff, since the static pages/index page you should be able to do yourself.
So what you want to do is start by creating a couple of parent categories. One of these parents should be "blog" and the other should be "portfolio". You should separate all other categories into these sections (unless you want stuff that won't appear in either category - then create categories for those too).
So say your "blog" are will have a news section, a rants section, a personal section. The "portfolio" will have your work, like illustrations, graphical buttons, and digital art. So you want to set up your categories like so (ID's in parentheses):
(1)Blog
(3)-News
(4)-Rants
(5)-Personal
(2)Portfolio
(6)-Illustrations
(7)-Graphical Buttons
(8)-Digital Art
So you see that "Blog" and "Portfolio" are the parents categories, and everything else is subbed based on that.
So, when you want to display your stuff, in the index.php file, you add in your code:
<php if(is_category('1') || in_category('1')) {
if(is_category('2') || in_category('2')) continue;
//stuff for post display here
} else { //start showing the portfolio stuff
if(is_category('1') || in_category('1')) continue;
//stuff for post display here
}
?>
So see, that says "If you're in the "Blog" section, and if the posts are in the "Portfolio" section, skip them." So you're still in the Blog category, but it's skipping over the portfolio stuff and just displaying the blog stuff - ELSE - if you're on the Portfolio pages, then don't display any of the Blog stuff.
Man, I know it's confusing, but I hope it makes sense (and answers your question!) You might have to edit that to refine it a bit, but it should work. Please note my bit of "frazzledness", as I'm doing ten things at once (and two of them involve children under the age of four) - so if I've skipped over anything..well forgive me LOL