i)"Requires" is a bit harsh LED's can be driven w/ constant current or constant voltage. CC is preferred..and yes a constant current driver is basically a voltage regulator that senses current and adjusts accordingly.
ii)same as if there are 3. Driver will ramp up voltage till it senses 1A..if .5v-12V @1A is the limit it may have a hard time doing 4 since the 3v is not set in stone. Natural variation ect may have the v(f) at 1000mA go beyond 3 v for each..
"A man with a watch knows what time it is. A man with two watches is never sure."