I think the bug thing depends largely on where you live. I'm in WI and have never had a problem with bugs and starched fabric -- ever -- but I mention it because some people in warm humid climates are adamant about not storing starched fabric.
How fast spray starch sinks in depends a lot on the fabric. Unwashed fabric has surface treatments that can slow down absorption of liquids, including starch, so starch has a tendency to sit on the surface for awhile. Washed fabric will absorb starch faster.
I don't use spray starch often. For the most part, I heavily starch yardage before cutting, using a 1:1 solution of Sta-Flo liquid laundry starch and water. I "paint" this solution onto the yardage with a large wall painting brush (reserved for this use!) until the yardage is saturated, toss in the dryer, then iron with steam. This is my standard treatment for all backing fabrics, foundation blocks for machine applique, and fabric that will be cut on the bias.
On the few occasions I use spray starch, I am very careful about overspray and will put a towel down in front of the ironing board to catch it. I am also very careful of iron temperature, because I have scorched spray starch by not waiting long enough for it to sink into the fabric. It probably takes just a few minutes for spray starch to penetrate fabric, but it always seems like forever to me when I am at the ironing board and impatient to get going! That's why I like pre-starched fabric. It is easily re-activated with steam or a burst of water spray.