Sorry if this is a dumb question but it's not everyday that I buy a new Mac, so I'm not sure how this works. I'm ready to buy an iMac but the Apple Store is telling me it's not available for in-store pick-up until August 15th. I'm getting the base 21" 4K version but upgrading the RAM (16GB) and to an SSD (512GB). Does customizing a new iMac always cause a delay or is stock for the new iMacs is very limited at this moment? Will this specific configuration eventually be available at stores or ready for immediate shipping?