"is adding tax-free bonds a good/bad idea assuming i might want to access the funds in 3-5 years"
In this case, yes! You probably don't want to put money you need in 3 years in the stock market, and you want to keep your taxable account tax efficient so tax free bonds make sense in this case. The other thing to consider is your tax rate. If you're in a low tax rate you are probably better off using a taxable bond fund, paying the taxes, and still ending up with a higher yield than the munis.
I personally wouldn't use VWAHX, the High Yield tax exempt. It handled 2008 better than most high-yield bond funds, but I'm concerned about the finances of several states and cities, especially if we went through another severe recession. I'm specifically worried about the states&cities with unfunded pensions, the ones that already struggle to pay their bills, and the places where their tax base is leaving.
If you look through the bonds in VWAHX you will keep seeing the words, "Illinois, Chicago, Kentucky, New Jersey, and Puerto Rico."
Pension funding levels:
Illinois: 36%
Kentucky: 31%
New Jersey: 31%
Everyone here understands compounding. If you are 1/3 funded for retirement on the day you retire things are going to get ugly, especially if your portfolio takes a big hit in a recession.
Credit ratings:
Illinois: 1 level above junk (Baa3)
Chicago: Junk (Ba1)
Puerto Rico: Junk (D)
I hope they are all fine, but if they end up not being fine I wouldn't want the money I need within 3 years tied up in these municipalities.
Side note: You can only add 10k/yr, but iBonds can also be a good parking place. The taxes on the interest are deferred until you cash out, and once FIRE you will likely be in a lower tax bracket.