Website + blog + webapp workflow

Hi, I have a website with a blog as an introduction to a web application. I want to migrate this to Grav. What would be the best practice to do that? I get the part of static content and the blog with grav, but, where would be the best location for the webapp code? maybe as a plugin? then, where would be located all the media (css, imgs, js) for this application?

You can put plugin-like logic in the theme. The theme class actually supports every event (except onPluginsIntialized), however, it's probably better to create a custom plugin. Check out the devtools plugin for a quick way to create a plugin. Follow the plugin tutorial on the learn docs and you'll be creating custom logic before you know it! Hop on our Slack chat if you need some help.

do you think that beeing a big application would it fit into grav, or may be is better to leave it alone, and integrate it in some other way?

My personal website includes static content and a blog. I'm currently building a pastebin into it, and will then be merging my family recipe site into it as well.

It's certainly doable, and isn't even particularly hard. @rhukster's suggestion of using a custom plugin is how I'm handling the parts of the application that require a little more freedom than a standard grav page would give.