I would say this face is entirely possible if you are willing to do it with less than 500 pictures. Some faces start to get a bit laggy at times when working with more than 100 layers depending on the file size of the layer and what kind of coding goes into each one. You could have it change once a minute if you wanted to or you could set it to have a random one appear each time the watch wakes up (You will get duplicates but it should be different most of the time). That is up to you to decide.
As for the sizing. If you want them all to fit perfectly they would need to be adjusted manually. Facer creator will adjust it to where it will fit on the screen but It wont fit properly the way you will probably want it to if you don't adjust it to the sizes you mentioned.