No Theme Blog Page With Categories

Hello,

This is a general question regarding whether or not to use a theme in a simple blog incorporated into an already existing web page. So I put all the WordPress content in a subfolder entitled ‘blog’ and have it working with the database. What I want is to have a simple blog page using the same styles, html, and css – I’m using Boostrap 3.0 – as I am using with the rest of the site. I want it to show the blogs as well as categories for each blog. Would it be easier to not use a theme, include the WordPress header and pull all this content individually into the index.php page using loops and then include the footer/headers and styles into the index.php page that I am using with the rest of the site? Would this work with categories as well? If so how would this work when selecting a category, does the index.php page dynamically re-populate with the blogs posts for that category once its selected – using the same index.php that has all the site styles included – or do I need to make a separate php file? I was easily able to include a title and excerpt loop into my original site, showing the posts on my top level index.php file. I just don’t know if it’s that easy to include all the information and categories into the index.php WordPress page without having to create a custom theme. Let me know!!