Bifen IT is a good choice for bagworm control. The product label recommends mixing at the rate of 1 oz per 1000 sq ft in approximately 1 gallon of water. Bifen XTS is an oil-based insecticide that is only for outdoor use, while Bifen IT is water-based and has a broader label. However, it is important to start control methods before infestation occurs. Once the bagworms have matured and have formed the "bag" most chemical control methods will no longer work.
Once the bags have formed, you can manually control bagworms by simply plucking them off of the infested trees and dropping them into a bucket of soapy water or squishing them.
As long as Bifen IT was applied as directed on the label and watered in as required for chinch bugs (at least 0.25 inch of irrigation) after application, you can go ahead and water in the fertilizer. It will not move much farther into the soil as it is designed to bind to the soil. If more water was used that would just have pushed it down into the soil better and will be fine.
An adjustable tip on your sprayer would be preferred when applying Bifen IT to interior cracks and crevices.
It will depend on what you are applying it for. For instance, if you are trying to control insects that walk on the blades of grass or around the thatch layer, if you use too much water, you could push all of the product below the thatch and those insects may not be affected by the application. If you are targeting insects that are below the thatch such as chinch bugs, more water can help you get the water where you need it to be. Please refer to the Bifen IT product label for complete instructions on your target pest.