I'm a 13 year old who aspires to be a filmmaker, but I don't have money to spend on software. Luckily, Blender is free, and so is HitFilm Express 2017. I know Express doesn't support 3d models, so is there a way I could still use both programs?
The answer depends a little of what you want to do, but your workflow will usually be to generate video sequences in blender and the export them to the video format you need to edit them in hitfilm. You dont need to support 3D model in HitFilm since blender can export video sequences.
For an animation movie, you just render your sequence and use it as such in hitfilm.
For special effect, blender has a lot of tools that allows to integrate 3D objects in a video,camera tracking, green screen masking, ... You will import a video in blender (a movie sequence) and add 3D item in the scene, using camera tracking to keep the orientation of the blender camera consistent with the "real life "camera used to make this sequence. You will use masking to keep a part of your real life object to integrate it in a 3D scene. You will use object tracking to identify the position of a real life element to attach a 3D object, like a gun to a hand.
Blender can do all of this so the choice of HitFilm won't restrict you for the 3D parts. Only for the editing/compositing part.