First of all, a gentle reminder, you have to be very tactful
when you have decided / felt in love with someone who you meet, see
and work together for most of the time under the same roof.
If you succeed, congratulations but you need to know the
do's and don'ts at the boundary line between colleague and girl
friend. If you fail, it would be a very tough for you to face her
everyday and if both of you are from the same department, the
condition would be even worse. Eventually, one of you may choose to
leave the company.
To answer your questions:
<> Not so difficult as both of you are colleagues, whether
you want or not, you two will have a chance to work together.
Moreover, when you see each other everyday, you can greet her to
break the ice. 
<> Not so difficult as there are a lot of areas of interest
as both of you are colleague. Ask her about her opinions about
certain issues that occur in the company. Also, question like "hi,
which department you are working for as I used to see you somewhere
around". Simple, you can ask something related to her works.
<> This is not so straightforward. But, since both of you are
in the company, just try to join the lunch group which she used to
join in. However, this is just a beginning. Then slowly, you can
have a chance to talk to / know her closely. First of all, you must
try to figure / find out whether she has a boy friend, otherwise
you are just wasting you times. Be patient and don't ask her out so
quickly, unless otherwise hinted by her. Take times and slowly,
when there is a chance, then you ask her out. 
<> There is no such high or low profile if she finally
accepts you. Why? No matter what, the other colleagues will know
about this relationship. It's ok. There is nothing to hide, so long
as you know the border line (work vs relationship).
However, the most difficult part is when the relationship
breaks up, you need to know how to handle it and facing her when in
front of others. 
<> Well, so long as she is not married or her boy friend is
not in the same company, I would say it is a healthy relationsip.
However, as I said, the most difficult part is how to convert the
'healthy love relationship' to a 'healthy working relationship' if
the love relationship fails or she rejects you... but touch wood.
It's a very difficult situation but worth to think about it now.
Good luck to you!
