Personally I do not like adding anymore sand in the succulent mix, since it may just turn too compacted later and the fine roots will just suffocate. I add some more perlite or pumice, to keep it open and well draining. I don't put river rocks at the bottom of my containers either..we all have our own preferences,some do it , some don't. I put a screen at the bottom hole though to save the soil.
If it is raining a lot and you have no protected area outdoors, then better have them indoors for now, till conditions improve and go warmer. Sure you can put them under growlights, just observe if the leaves are getting too toasted/dried up, you may have to adjust distance from the light. Cacti likes more light, these other succulents are okay with just bright/dappled light, so adjust the distance/location of your plants as needed.
