3D Printing Questions on 3D printed dolls as buyer not maker

I'm only just starting to take an interest in 3D printed dolls, most notably I've seen some interesting doll files on Etsy, etc. However I do not have much knowledge on 3D printing nor do I own a printer. It looks like there are plenty of places online that do printing, however, how do I determine what would be the right place to go with? What should I be looking for so that my doll turns out high quality?

Also, several of the makers do not specify the doll's size. They are STL files and I'm wondering would I have a choice in scale from a 3D printing service? Can I print a custom height and if so, how would I determine what scale is too big or too small? I'm just not sure how this works.

If I just wanted to look at the 3D doll, what program(preferably free) could I use to do that? Would it be possible to see how the details could be lost at certain sizes in it?

Thanks so much, this is something I've only recently become interested in and it's fairly overwhelming but I'm intrigued.