I have both the baby Cricut (6x12 mats) and Cricut Expression (12x12 and 12x24 mats) . If you intend to purchase the princess cartridges, I would highly suggest you go with the Cricut Expression. I am in a swap now making 25 Mulan's and Mushu's. I am cutting mine at 10 1/2" and the eyes/mouth pieces are so small. You would not be able to do this on the baby Cricut very easily. Also, baby Cricut cuts the images horizontally, not vertically, so when you say 5" that is the height of the character. With the Expression, you can tell it which direction you want - Landscape or Portrait. I mix it up to make my mats last longer. Also the Expression has a feature to pick a cut and then tell it the quantity you want like 25, it then estimates how many it can cut and tells you say it will cut say 6 times. When it is done with that mat, put in another and it will cut another 6 and continues on until it reaches 25.
Both machines can use the Cricut Studio software. I haven't had time to play with it much, but it can be used on both machines. When you buy it it comes with a USB cable, mouse pad and software. I have to play with it this weekend to see if I can only cut out the mouth for Mulan. When I did the cuts, the sleeves and dress came out fine, but the lips tore...I don't need the dress pieces any more so I am going to try to use the software to just cut the lips again.
I am also in another swap for Ariel, Sebastian and Flounder. I haven't started on them yet. But I would think the Expression would help with the eyes.
If you look at the Princess cartridges, there is a warning that some images can't be cut on the baby Cricut. That is just the limitation of the machine.