You can have even volume when switching from the humbucker to the singles. Its dependent on the output of the pickups. Match them well, no volume issues.
But even if even volume is achieved, there will be a difference - the humbucker usually sounds fatter, thicker, and the singles will be thinner sounding.
So far, my favourite setup is a low output 8.4k Alnico 2 bridge humbucker (HighOrder Pickups) and 2 Bill Lawrence L200 single coils. All hum-canceling. This setup is excellent for bluesy playing all the way to hard rock. Little compression so excellent dynamics and the cleans shine very nicely. Not the best choice if one likes to do metal or needs a certain amount of compression.