I'm addressing the question on the subject line, because I'm just now on the cusp.
When I first came out to myself, I planned to wait until I passed before going full-time -- meaning until I had had FFS & VFS, which I didn't know when I would be able to afford. I was so innocent.

I started changing little things in my presentation almost immediately. From time to time, I would find that I had to increase it; I didn't really have a choice. I mean, I *could* have resisted it, I suppose, at a cost to my own emotional well-being. I needed it -- I needed to express my femininity.
Eventually, I crossed some sort of line because people started giving me looks. But by that time I had built up a well of self-confidence. I was able to go out in public with a presentation that would have terrified me in the beginning.
I'm changing my name this month. Most of the people I deal with on a regular basis know me by my female name already, the one exception being my boss at my full-time job. When I get the paperwork, new ID and new SS card, I'll let him know then, at the latest. Just recently, I began going out more regularly in full female mode. Believe it or not, being clumsy with wigs and makeup have been as much of a disincentive as social anxiety; but recently I just bit the bullet and did it anyway. Just today, I went shopping at a big box store, wearing a denim outfit, boots with heels and showing my figure (I usually wear a sports bra). Now, I clearly don't pass; no one who looks at me mistakes me for cis. But one of the male employees addressed me as "ma'am" anyway. What a sweetie.

Maybe you'll be like me and just find you have no choice. Make it easy on yourself by starting now and starting slow. I think it will make it easier, when that day comes.