how to fill spaces between paths

hi !

i have a little question for illustrator cc, i dont find a solution to this on my own.

i am doing geometric drawings and mandala like stuff and draw lines for in different stroke sizes

and afterwards i wanna brush out the spaces i generate between the lines.

i dont wanna use the live paint bucket because i dont wanna just fill the spaces,

i wanna paint them out with a dots brush in a special way.

what i did till now was to redraw the spaces with the pen tool on a new layer, which

is sooo much work and i thought there must be a simpler way.

i tried with the outline stroke, but then the outline stroke is not at the edge of for example

a 7 pt stroke, but the outline stroke then is much smaller and not on the edge of the thick stroke.

please excuse my poor english by the way, i do my best !

so i checked out the pathfinder, didnt really work.

i uploaded an example here:

https://ibb.co/b4eane

i wanna brush out the empty spaces in the drawing with a brush..

i hope i made myself clear and would be thankful for any help,

all the best

cris