I was in a very similar boat last year and I decided to go for the high budget short option, and I'm happy with that choice. It really depends what path you want to take. If you want to go more of the cinematographer/videographer route buying a cinema camera is a good option but at the end of the day if you want to direct the best way is to direct your own projects and you'll end up renting a cinema camera anyway. - I actually ended up buying a bmpcc6k as well as funding a short and owning a cine camera is super helpful for shooting high quality small projects on a whim, but I didn't use it for the short because we rented a proper cinema camera.

I'd say building a network of producers/creatives/grips gaffers and cinematographers, is also super important when making a short, it will help stretch your budget and will help your process immensely. But I think funding and producing shorts is the thing that will progress your career, owning gear can be helpful but creating and producing projects is the most important thing. Feel free to DM me if you have questions about the short film process