It is hard to predict. Render time is divided on two pieces: a preparation (resolution independent) and an actual rendering (depends on resolution mostly). Second part, typically in quadratic dependence on size. If you make the image 50% instead of 100%, it will make render time of this part 4 times faster. This is because the render image is 2-dimentional, ...
Are you sure your Sun is named "Sun" and not something like "Sun.001" ? Are you sure there is a sun in your scene? You can also access objects by their index instead of their name. For example, if your sun is the fourth object in the scene, you may be able to access it with Sunobj = bpy.data.objects
In compositing: connect your image from Render layers to denoise.
Hint: Always make a render at least from one frame before rendering a
movie. And by the way: you shouldn't render directly in a movie but
render in PNG or any other picture format of your choice. So whenever
Blender crasher you can resume rendering and safe tons of time.
You can use the glare node to get the same effect, along with some adjustments if you want to modify the strength or give the bloom a uniform color.
You can also use the "greater than" math node to extract the bright parts of an image, blur them, and add them back together. The result however isn't as pretty as the method above.
The problem is caused by the Mix factor in the Glare node in the compositor. From the Glare node documentation:
Value to control how much of the effect is added on to the image. A value of -1 would give just the original image, 0 gives a 50/50 mix, and 1 gives just the effect.
Currently the Mix value is set to 1. Setting it to 0 will solve the issue.
The answer, as with all performance questions, is "it depends". I can go into a lot of detail about what it depends on, but Duarte Farrajota Ramos' comment nothing like a good old test is the only reliable way to get an answer.
There is a cost to using image textures, even in terms of GPU VRAM usage, but even it is difficult to quantify because it ...
Blender doesn't render vertices, it renders faces. If you only have vertices with no faces being drawn between them, there's nothing to render.
But you could instanciate a small sphere on each vertex, then the sphere instances would show up in the render.
To answer your comment with images...
Change that 40k number to something that your PC can handle, like 1000 or something
Then go down to Children
Click on Interpolated and add value 40 here:
I choose 40 because if you have Number set to 1000 and interpolated to 40, it basically means that every single 1 grass will be rendered as 40 strands of grass... (...