I've only been doing this a couple years, so I don't have too much to add but thought I'd chip in on a couple things I do.
1. I always test for HT in the same circumstances (I use my bathrooms because I have dogs and a kiddo and I can shut the vent without impact to the house)
2. I don't try to wick the container unscented since I don't sell unscented - so I'm really just concerned with the right size wick for the right scent. I typically start with my standard wick size and only mess around if it's not performing as expected with that scent. And honestly, there have only been a couple times I've had to wick up or down and I didn't end up doing anything with those because I wasn't getting the burn I wanted (ie, they were over or underwicked).
3. I do one entire test burn of a candle trimming the wick, and another entire test burn of a whole candle without trimming, and incorporate a power burn (6+ hours) into each of those tests.
I will also say that I really don't add many fragrances to my line - I know there are lots of makers on here that have tons and tons of scents, but I rarely add anything new. I did a ton of testing to get to the scents I have now, and I just keep using those. Although now I am reordering I have to retest since the reformulation of many oils.