I find that maintaining "professional" relationships is fairly easy in my line of nursing. I, too, am not a big hugger and really hate it when I have gotten kissed (Once on the top of the head by a 85 year old husband of a patient - sweet? ewwww...) And I'm not that short.
On touching, hugging and such - I just try to keep a distance, but the inevitable does happen - in that case, I just kinda roll with it. I have had cases where what the patient/family wants is that hug and a shoulder to cry on and sometimes that is okay. I think that as compassionate human beings there are just times that we will need to lean on others - nurses are not exempt. Although hugging and holding are somewhat intimate, it is not sexual or sensual --- Big Difference.
Signs its becoming ... well, too much. If you think it is, then it is. Boundaries need to be set, but ... they need to be well defined and enforced to work.
As to personal involvement? Being invited to meet for a book club (when you are new in town) because you have discussed a book being read by a family member is not a problem. Also, when known to be "new" in town and obvious of faith - being asked to attend worship is not a problem.
Going to deliver (leave in stealth fashion/odd hour) a bag of groceries/diapers/case of formula to a single mom - that had her sick really kiddo in the ED and has some serious financial issues and 4 kiddos under 3 years old - is probably crossing a line (but, sometimes ... allowing for assistance with letting someone keep a little pride is a good thing).
Being "set up" because your patient has "the best grandson" and "he'd just love you" - awkward and probably not a good idea, but... I'd just always reply that I have a boyfriend. So be prepared - that has happened to me on several occasions and although I wasn't married (and even now that I'm married - I don't wear a ring at work) "I don't see a ring, dear" - I always have a good answer.
Now, going out on a date with a patient/former patient. I say its just bad mojo - what if it doesn't work out? what if they remain a patient? what if it goes just plain psycho bad and you get a complaint filed on you at the BOARD of NURSING. I say why risk it? There are lots of fish in the sea, just keeping casting away - but avoid the work pool!
Good Luck, and remember that if you think it might be/feel/look inappropriate - then it most likely is.