Hi riesta,
I'm glad I could help.
Regarding your second question, you should:
1. Create the local variables MinValue and MaxValue to store the values of the slider and also set their default value to 1 and 20 to keep your use case;
2. Add the filters on the query to take into account the variables MinValue and MaxValue
3. On your action RangeSliderIntervalOnChange, a) add the assign MinValue = SelectedMinValue and MaxValue = SelectedMaxValue, b) refresh the query c) AJAX refresh the widget you have on the screen binded to the query.
Cheers,
João