boyerbt (original poster) - Roth IRA has a contribution and growth part. Whatever your originally put in is the amount you can take out at any time with no taxes. When you put $5,500 in you can take that out at any time. If that $5,500 Roth grows to $7,500 then you have $2,000 of growth. The growth has to remain in the account until you satisfy IRS rules like age 59.5.

As to taxable investing, you want to minimize tax. Bonds throw off ordinary income, so that's the worst thing to have in taxable... but tax-exempt bonds can solve that problem. I prefer to minimize taxable yield, which means picking US stock funds over international stock funds. Take your qualified dividends tax rate (probably 15%) and multiply it by the US (~2%) and international (~3%) yields to see how much tax you'd pay. The foreign tax credit is a bit tricky to calculate, but I believe it doesn't completely offset the higher tax that comes from a higher yield. In any event it's a small difference, so consider mixing international and US in taxable for rebalance purposes.

Note if retiring at roughly age ~55, you only need ~5 years of expenses before you access everything with a 59.5 age restriction. You might only need a fraction of your assets in taxable to make this work. You can also use a Roth conversion ladder to make more assets available before 59.5.

Guide2003 - That's unusual. Tax rates below 10% favor using a Roth IRA.