I would agree that if possible stick to 36ga or higher (thinner) wire for the wrap. A lot of people use a rule of thumb of 8-10ga sizes difference between core and wrap, which I agree with to some extent. 28/38, 26/36. However if using 22ga cores I wouldn't use 30ga for the wraps personally. Too much wire mass makes for either slow ramp up or setting wattage higher than desired to overcome the slow ramp up and the result is a blazing hot coil. The thicker the wraps the longer the coils hold the heat too, so after you've taken a puff the coils stay hot cooking the wicks/juice. Been my experience anyway.
Definitely finer wraps for finer core wires. I see a lot of premade (machine made) stuff with odd pairings like 28/30 or 28/32. Maybe it's easier for their machines to work with. Thicker the wrap the stiffer it is and if trying to wrap multiple finer cores the stiffer/thicker wrap is more likely to twist the cores or cause them to collapse together. Finer wrap wire is a bit trickier to see but bends much easier and more suited to the finer edge of thinner core wires. (As the cores rotate, the edge will only be the thickness of a single core wire creating a tighter bend for the wrap).
Not sure if my eyesight's gone to crap or if 38ga really is difficult to see while winding. Either way I used a pair of lighted magnifier glasses like they sell for jewelry work. There's cheap ones for $10-14 on ebay, comes with a variety of lenses with different magnification. Granted once things are spinning it's harder to see each wrap but still makes it easier to see that they're not backtracking and winding onto each other or make sure there's no gaps and the wrap's laying nicely against itself.