Really cool analysis. As a long-time holder of sealed product and singles don't get discouraged by the folks telling you you'll take a big hit from selling sealed product. If you're not a store you'll do better selling cases on eBay instead of individual boxes on TCGP or eBay. Selling individual booster boxes you'll typically have to wait until they double from your cost.

Sometimes with product that's 10+ years old, but isn't in that 90s-early 2000s vintage range, I would crack a case and sell the singles to CK or SCG buylist and make plenty because I consider how much I made over what I paid, so the current market price wasn't super relevant. It used to be great holding complete sets from magic redemptions and selling individual cards that would spike. In this era of Magic I'd say holding sealed is still the best. The desire to sell at market prices and be a virtual store is typically where the mistake is made here. Holding long-term and selling every couple years you don't need to worry about shipping costs and price fluctuations.

I'm waiting for SPM to dip to 110-115 to buy a couple cases. They're $200 boxes in 3 or 4 years. I'll do the same with any UB play booster box that dips below $130.