You have a custom rifle, so I would expect that the barrel is installed parallel to the receiver. Barrel vibration should not be too bad with a heavy profile barrel, so the live fire 100 yd zero should be within 10 MOA of boresight. I would go with the 30 MOA base. Worse case is that you may need to zero at a longer range.
That will leave you with approximately 70 MOA of up adjustment, which is in the ball park of what you need to get to 1500 yds, depending on load and altitude. Your zero should be within one turn or so from the limit stop, so finding your zero will be easy.
I recommend that you not leave the scope elevation set for your zero range during storage. That setting has the erector tube spring nearly fully compressed, which could weaken the spring over time. Better to leave the turret set to the mechanical zero or even closer to the long range limit stop. Then set it to zero when you pull it out of the case to start shooting.