Make sure bloom is enabled on render Eevee render and you are rendering with a black background. Rendering on transparent background will cause the bloom to be gone on the exported image.  If you're using Cycles render, you must need to set a bloom effect manually using the compositor.

Yes. On the .blend file you have a node material called "image as plain - firework". Only you need to do is import the image to image texture node.

Yes. Each firework is a particle system ready to you for manipulate and use for animations.

You can use Eevee and Cycles.