We have a donor advised fund with Vanguard Charitable, very happy with DAF, Vanguard Charitable, giving to charity etc.
I'll add one anecdote about the timing of large contributions: we made the initial minimum $25k contribution in our second last working year, assuming it would be our highest income, most tax efficient, etc. The plan was that in our last working year, we would make some smaller contribution, based on the exact amount of income we made that year (once you open a DAF with VG Charitable, additional contributions can be as small as $5,000)
However, I found that in our last working year, with all the different balls in the air after FIREing, I never found time to do the exact calculation to see how much I wanted to contribute, and to my embarrassment, after both of us quitting our jobs, I got uncomfortable with the idea of making another not-even-that-large contribution in that year (with hindsight, stock market soared, we made more income in retirement, and spent less than planned.. we could easily have afforded it, but psychologically was hard at that time)
So I'm glad we made that large contribution in our second last working year, when we didn't even shrug it off, and got it out of the way.