What are the considerations for veterans serving with a disability rating? How do you navigate staying deployable, ACFT ready etc?

Fitness for entry into service, Fitness for duty, Fitness for continued service/retention, and Fitness for separation are all Title 10 requirements and should not be confused with Title 38 VA rated disabilities. You can be rated by the VA and still be fit for duty and vice versa. They are two separate standards.

From my limited understanding, there is not a magic percentage that limits your ability to continue to serve. I personally know a couple of Service Members that are rated at 100% disability but still wear the uniform. Where the issue rises, is when the disability effects your ability to perform. For example, if I have a disability rating for hearing loss, depending on severity, my PUHLES may read as 112111 which would allow me to continue to serve in most military positions. However, if I have a an award for a lower leg disability, depending on severity, my PUHLES may be 111211, which would remove my ability to serve in many positions in the Army due to mobility issues.

If your disability is severe enough to gain you a 3 in your PUHLES, then a MED board is recommended and they will determine your ability to continue to serve.

So, if you want to serve with a disability rating, continue to train as you fight within the your capabilities and without breaking your profile

I think it would depend on what your overall rating is and what the disabilities are.