Congratulations on your pick-up!
Spare parts - AMMO!
The proprietary parts are not an issue to me personally, I have yet to see an E3 Bolt fail.
I honestly haven’t run into an issue yet, but I have seen some ejector spring fail on the forums but that is after 10’s of thousands of rounds. But it is always a good idea to keeep spares on hand if you can afford them....
Enjoy shooting that beauty