Reserve retirement plus FERPA

I am a MD student and am in the process of potentially joining the National Guard later this year to help pay for it; physician incentives include stipends while in school and residency and loan repayment. I also plan to work for the VA after I'm done with residency training if I end up joining the NG.

Someone explain to me like I'm an idiot how this works with a dual retirement? I'd essentially be retiring from the NG anyway based on service commitments for the incentive programs and VA would be a good career to absorb potential deployments and other military obligations.

Would I basically get both the full FERPA and whatever reserve retirement I accrue based on points? Is it split in some way? How does payback work if I have active time via deployments etc, does that get removed from my reserve retirement points calculation and directly added to my seniority at the VA? Can you buyback multiple times or is it a one time only thing, like if I go on a deployment 5 years into working at the VA could I cash that in or nah? I can't really find an easily digestible writeup on this.