Roth IRAs have two parts.
When you contribute $5,500 to a Roth IRA, your "contributions" are $5,500. You can take out that exact amount in the future, with no penalty. The other part is growth: if that $5,500 grows to $6,000 you have $500 worth of growth. The growth needs to be left in the Roth IRA until age 59.5, and is penalized if removed early.
At higher incomes, you can't contribute to a Roth IRA. I'd guess you can only contribute for 1-3 years, and so have $16,500 worth of contributions (max $5,500/year). Since you aren't retiring on $16,500 I'd take advantage of the tax benefit but otherwise not count on the money in the Roth IRA for retirement. You will need something that can hold more.
Oh, and you might want to check out "White Coat Investor" - either the book or the website