Actually, "to" and "toto/tohle" does not indicate distance, but actual physical presence at the moment of the conversation. For example: if we are talking about that girl over there, on the next bench, we would use "toto/tohle": "Jak vysoke je toto devce?". Meaning something like "how tall is that girl (that's right over there)?". On the other hand, if we are talking about my colleague, at work, with which I would like to hook you up (but you haven't yet met), you might ask "Jak vysoke je to devce", meaning "How tall is this girl (that you are talking about)?"
No. 'Dívka' is synonymous to 'děvče.' In terms of formality, 'děvče' is the most formal and slightly bookish, then 'dívka', then 'holka,' which is pretty informal.
For information about creating plurals, please consult the tips & notes or Wikipedia or Google.