Even as long as I have been making my own e-liquid I don't think I would be comfortable working with anything above 100mg but that is just me. Like
@englishmick I also mix mine down. I take a bottle of 100mg out of the freezer, bring it to room temp and then cut it in half so most of the time I am working with 50mg. I always keep a 60ml bottle of several different strengths mixed up (12, 16, 18 and 24) for playing around with.
@DogDriver Please be very careful with that 200mg. You need to be in a well ventilated room and be close to a water source in case of a spill. The first time I transferred my 100mg to smaller bottles for freezing I had a fan behind me blowing toward my opened kitchen window. I don't know that something like that is necessary but it gave me peace of mind.