What should I know about storing my homemade chili powder?
From experience I'd say those 6 months don't stack. You could have 6 months in the jar, or 6 months in the freezer - very soon after defrosting the flavour would die out. If you have to freeze I would recommend using it straight from the freezer, if you can avoid it clumping.

The overall potency is degrading from the moment it's picked! But realistically from the moment of grinding, as the oils in the ingredient are slowly seeping and evaporating out of the grain.

Why not make smaller batches more regularly? That's what I do for garam masala, mixing a new batch every 3 months or so.

I would always recommend oven drying spices / peppers very low for a long time - say 2 - 3 hours at 100C (212F). Wet ingredients could be dried in the same way, else added at the time you are going to cook with them.