When I started transitioning, but before going full-time, I did more or less the same as you - gradually started presenting more female, but letting people make up their own minds. Loos - well those were always kinda tricky, and for a while I just snuck into disabled toilets. As you say though, being friendly and engaging and confident makes a HUGE difference.
At work though I don't think there is any middle ground. I worked as and presented as fully male as I could, even though my hair was growing and such, till I no longer could pass effectively as male anymore. At that point I was due to come home to South Africa anyway, (I was in London for two years) so I finished my contract, came home and went full time. Having built up some savings, and after testing the waters as an "out TS looking for work", I decided to take a few months to finish my legal transition with name change and all the rest of it so I can start with a clean slate in January. I think that, if you intend to stay where you work, the only practical way to do it is to go away for a while and come back as a different person. Trying to gradually ease into things while not giving too much away - I tried that for a little bit in my private and social life, and it kinda doesn't work. People who know you need to know where they stand with you - I find that people are less uncomfortable with knowing I'm TS than with not knowing what I am, generally. I came out to my family and friends long before I started transitioning, and I just never muddied the issue for people at work - they just thought I was a (very) femmy gay boy. They had me in a box they were comfortable with, instead of me moving the target on them.
Hope it helps hon.
~Simone.