What tweaks can be made when preparing chili powder?
First, as someone who has made chili powder, let me offer you one piece of advice -- get yourself a coffee or spice grinder.

Second, disabuse yourself of any notion of making your chili powder with anything wet. Whatever goes in should be bone dry. I wouldn't even bother with drying fresh peppers, garlic, etc. It's just not worth the effort. However, you absolutely should get your cumin in (dried) seed form, and dry toast it yourself. That IS worth the effort.

Beyond that, everything else is negotiable. Mess around with different types of peppers, different herbs/spices, different proportions, etc., and see what you like best.