Fourth, I volunteer often in the US and abroad and spend tens of thousands of dollars on mission projects, which is another variable I need to account for. Knowing all this, does it make sense to FIRE when one turns 47 ? Maybe I am having the "One more year syndrome" - not sure. Your thoughts please ?
Financial projections aside for a moment, why do you want to retire?
Serious question-- you're doing something you enjoy, it's fulfilling, it's complex. The only thing lacking may be autonomy, and you could certainly gain more of that through going part-time.
Otherwise you're going to have to put yourself on a strict philanthropic budget, which means that someone isn't going to get something that you can see (because they're standing right in front of you) they desperately need. At that point I'd find it difficult to say "I'm sorry, I've already spent my 4.36% SWR, but I'll be back in eight months with next year's funds."
Maybe you need to somehow become part of a non-profit that pays you a stipend (or at least matches your philanthropy) and lets you spend all your time volunteering on missions. Or maybe whoever's paying your salary now could instead put you in charge of their new philanthropic department at no cost to them. You could work 20 hours/week or six months/year for them, bill them for your time, and instead of paying you a salary they put the money into their charity fund. Then you could spend the other half of the year representing them (and spending their charity fund, not yours) on the missions you'd be doing anyway.
You can't be the first doctor to encounter this situation. Some other doctor must have already solved the problem, or at least their CPA did.
How to psychologically switch from a "saving mode" to a "withdrawing mode".
But getting back to your original question, you'd pay yourself a "salary". Figure out how much needs to be in your checking account each month and put that in auto-transfer from your portfolio. Check your portfolio occasionally for rebalancing, and set aside the cash for another year's spending. Then have that show up as "paychecks" in your checking account for you to spend until you reach your budgeted amounts.
We were a little tight on the purse strings when we first retired in 2002, but we were also in the middle of a recession. We were also trying out a number of new activities (like surfing) and we weren't sure we wanted to spend hundreds of dollars on the activity while we were still trying it out. As the months went by, though, we got comfortable and loosened up. The same gradual transition will probably occur with you.