What program are you hoping to use? Have you even picked one yet?
CGI is an outdated term these days, but decent modelling programs cost anywhere between 0 - thousands. Are you planning on spending money buying industry standard software, or are you only going to learn open source? What about your budget for learning - any paid courses/books or all online tutorials?
I use Blender - it's free, open source and industry level 3D design, modelling and animation software.
blender.org - Home of the Blender project - Free and Open 3D Creation Software
Examples of what can be done with Blender:
Those four videos are all open source projects made by the Blender Foundation. AKA - if you have a team of expert designers/animators who are so proficient with the software they designed half of it, then you can make something like that reasonably quickly. Sintel, their third film, cost 400,000 euros and took over a year and a half to make a 15 minute film.
Here's an example of a non-professional film, by which I mean one that wasn't made by a paid team/the blender foundation.
Pigeon: Impossible - YouTube
That short film took someone over 5 years to produce, dedicating a significant amount of time to the project. If you're only having ships involved in your film, and no people, the animation time will be reduced (people/animals are a lot harder to animate), but a 2 hour film is way too ambitious. Even if you spend a lot of time learning the software and become good enough to theoretically make the film, you're looking at a significant investment in time just to make a much shorter film. It's not impossible, and if you're interested I'd encourage you to learn, but there is a reason why professional animation studios have large teams working on films.
There are plenty of resources for learning Blender - if you want to learn a different tool such as Maya or Poser, then you might have to pay a bit more for books/courses on learning. The best way to learn is to just do it - follow a couple of tutorials to learn the interface of whichever program and get a grasp of the basics, then try making gradually more details models/animations and set yourself short challenges. E.g., model and animate one moving part on the ship (aka a main gun or whatever) - make it look realistic and move realistically.
As a first goal? Aim to design, model and rig (not animate, just rig - aka adding moving parts to your model which can then be animated) a ship that could then be used in an animation. After that? Make another one and animate a short fight sequence between them. If that goes well, try and create an impressive wallpaper/photo of your two ships in battle - think about the lighting and textures, and try and make it look as detailed/realistic (or stylised) as possible.
Here's the Blender Artists community:
Blender Artists Community
Lots of examples there of modelling and animation.
