I'm new at this too. I steep by removing the caps of the juice bottles and letting them air out overnight but not more than 24 hours. Then I place the caps back on, shake them and leave them alone. I may test one of these new flavors after a couple of days, but if it still doesn't taste right, it goes back to the steep drawer until they become vapeable to me. My bottles have all been 30ml or less. You've probably already ascertained that each company's juices do not steep at the same rate. My very first juices I still cannot vape, they've been in the steep drawer for almost a month. I think this is all trial and error, plus each individual's subjectivity.
In regards to the throat burn, I was testing a bunch of juices this past weekend (new and old) and I had my first experience with throat burn. My juices are either 50/50 PG/VG or 65/35 PG/VG. I'm not sure why I had throat burn--maybe it was the chain vaping? I rarely lung inhale, but I wonder if the few times I did (with an "ice" flavor if that makes a difference), may be the reason. For background, I was dripping on 1.7 mircocoil, on an IGO-W, with my innokin MVP, 3.7V, 7.0 power.
Do your flavors contain menthol?