The Interactive Display Adjustment is one tricky part, similar to that inside Spyder software
You'll need to take a lot of time just to get the bars right
But once done, you're good to go
Actual calibration results also depends on environment, eg. how proper your room is lit
It's suggested that you turn off all lights prior to actual calibration
And yes it is important to understand every parameter setting under the Calibration dialogue
Set one thing wrong and your calibration may not continue or complete
Do however know that dispcalGUI/ArgyllCMS is freeware and constantly under development, so bugs are quite likely (even though you have all the settings right)
As for sRGB coverage, are your sure you've set your monitor to the right mode (eg. "sRGB")?
If not, do that again
For LCD displays, you will in most cases only want to adjust white point (if the screen has RGB gain or other whitepoint controls) and white level (with the white level also affecting the black level unless you have a local dimming LED model), as many LCDs lack the necessary "offset" controls to adjust the black point (and even if they happen to have them, they often change the overall color temperature, not only the black point). Also note that for most LCD screens, you should leave the "contrast" control at (factory) default.