I wouldn't suggest trying to comb your hair while it's flipped over. That would be very likely to cause knots, as you found out!
I would get rid of your brush entirely. While there are a few people who like to wet-brush and find it helps clump their hair into nice controlled curls, more typical is to find that brushing breaks the hair and pulls out the curl pattern.
Either fingercomb your hair or use a wide-toothed comb. Do this in the shower while the hair is full of conditioner, and the knots should come out without too much trouble.
Get rid of the hair spray. Hair sprays contain drying alcohols and drying propellants, and the resins don't rinse out and contribute to knotting.
I think you need a good styling product. Herbal Essences has three new gels that all are very good and inexpensive. Totally Twisted has a soft hold, while Body Envy and Set Me Up are stronger hold. You would need to experiment to see what works for you. There also is a Set Me Up spray gel which may substitute for hairspray but will rinse easily from your hair.
Some people like cream stylers, especially in winter when the hair tends to be dry. There are not a lot of good drugstore cream stylers, but you could try Dove Molding Cream, Garnier Fructis Soft Curl Cream, Samy Curls Define and Extend Cream, or Samy Smooth Reaction. (Of the two Samy creams, Smooth Reaction has more hold and I much prefer it to the Curls cream, but those who like a very natural hold may like Curls.)
I personally like to comb styling products through my hair with the wide-toothed comb, and then scrunch the curl pattern back in, but many people prefer to rake the product through with the fingers.
Curly Hair Solutions has one really outstanding product, Curl Keeper
, which is generally used in very small quantities as a substitute for serum, under other styling products. Their other products are okay but not outstanding for what you pay for them. Product lines that are much loved by NCers are Devacurl, Jessicurl, Curls and Curl Junkie.
Hope that gets you started!