Need 2 Post Pages for Grid Layout

Hi!
I am trying to come up with the best way to design a grid layout for a wordpress portfolio template. I’ve scoured the forums and haven’t been able to find a solution that works for my site. Please be warned that I’m a beginner, and my code probably looks abhorrent to those of you who actually know PHP!

What I am trying to do is create a layout that has a portfolio page, and a blog page. Currently, my portfolio page links to all of my posts, and shows thumbnails if the post has a featured image.

I like the idea of the portfolio page only displaying thumbnail posts, and having a regular blog page with a normal 2 column layout (content/sidebar). That way, the user of this theme could easily add to their portfolio by setting a featured image to a post.

But I’m realizing that in order to have a normal blog in addition to the portfolio page, I would have to have to have a loop that only includes thumbnail posts, and a loop that excludes thumbnail posts for the blog page. I don’t know if this is possible- from everything I’ve read… well, I’m confused. I was wondering if it’s possible to make an archives page that looks exactly like a 2 column blog page, showing full posts, and just use that as the blog page?

I hope my questions make sense! Anyone willing to help out a total beginner?

Here is what I have so far- My Site