I like the proposal with 4 suggestions:
1. The 75/25 is too risky. I would go to 60/40. The 60% in stocks according to your 2/1 ratio would be 40% US.
2. I would not presume that you have the skills (nobody does) to know when to switch from short to intermediate bonds. I would just go with intermediate. Frankly, the yield or the long term tax exempt is quite a bit more than intermediate and the duration is only 1 year more. Larry Swedroe or Rick Ferri, I don't remember who, believe that a 0.2% increment in yield for a year is worth going long for. It is about 3/4% now.
3. I would consider a single state muni fund if Vanguard has the one you want. (I do this with New Jersey)
4. VERY IMPORTANT-- if you are mostly cash now, I worry that you might panic if you go all in now.I was in a similar situation a year and a half ago and elected a 4-5 year averaging in period. I am glad I did as I might have gotten nervous now.
So here goes:
Total stock index admiral: 40$
Total international stock index admiral: 20%
Intermediate term (or long term or state specific long term) muni fund: 40%
Divide it up into 16 pieces and do it quarterly over 4 years.
Or 12 pieces and quarterly over 3 years.
Last, prepare for a discussion on dollar cost averaging vs lump sum investing unless you tell others to avoid it !!!