I’m fairly new to water adjustments. This in only my fourth batch with additions. One thing I notice is the additions don’t seem to dissolve. I added 9g gypsum, 4 g calcium chloride and 1 g epsom salt to ten gallons while warming the mash water. When I was done heating I could see a good bit at the bottom. Should I be crushing them finer first?
Usually adding to the boil does well to get them mixed.
If you're concerned about clumping you can take some of the hot wort into a cup and slurry the addition to add back to the kettle.
Adjusting strike and sparge water is only needed for adjusting pH. A complete water profile for a specific style of beer isn't critical at this stage.
I believe best practice is to add your minerals the night before brew day, make sure to stir vigorously. Any minerals that don't dissolve overnight should eventually dissolve as you're heating the water to strike temperature with a bit more stirring.
One notable exception is Calcium Carbonate (Chalk) will not reach desired concentrations in normal conditions. If you need to add calcium carbonate to achieve your mash water profile, you can dissolve it under pressure of CO2 in a keg.
The "Water" book by John Palmer and Colin Kaminski is really a must for anyone who wants to really understand what's going on with water chemistry in the brewing process. It's a bit dense, so it'll probably take a few reads through if you don't have a chemistry background.