Forget chili powder – the trick is using a mix of dried chiles, choosing from 3 or 4 types. Keep notes, and try different mixes to see what you really like. You can’t go wrong though.
The chiles from the “mild” list bring great flavor but not much heat. A can of chipotles in adobo adds some heat (and super flavor) — but for real heat include some of the hotter chiles in the mix. Just don’t go crazy unless you’re certain your audience wants it.
To find a variety of dried chiles you may need a specialty grocer, or fire up the intarwebs. Some mainstream grocery stores carry only one or two types — and you should check the expiration date.
Here is a list of dried chilis, sorted roughly by heat level — with links to buy them online. This is not a sponsored product placement, just a convenience. I have no relationship with these sources and don’t vouch for them. I buy my peppers at a local Hispanic specialty market (also a great place to get your chorizo!)