I think you need to read more about the different types of mutual funds and how they historically perform in different economic situations. I don't mean to sound harsh but equating Wellesley to an Index 500 fund, is like a new cook thinking salt and sugar can be substituted for each other because they are both fine white granules.
Spend a few months reading HumbleDollar.com. No need to rush. The fact that you have chosen a low-cost provider shows you are on the right track, something that most people can't say. You have a small knowledge gap to fill, then you can aim straight for the FIRE bullseye.