Nicotine definitely adds a flavor and produces harshness, so 0mg samples will likely not be representative of what it would truly taste like as long as you're above 3mg/mL. I mix my
juice at 1.5mg/mL (just started at that strength) and can't taste a thing from the nicotine. My 3mg batches produced a very slight flavor, and the 6mg batches were definitely noticeable in the difference between the 0mg samples and the mixed juice.
Steeping will bring out flavors more, it really depends in the flavors you use though. Steeping does different things to different juices. Just don't worry about it, experimentation is what DIY is all about!