I know this is shallow but the most important question to ask before getting married is, “will my marriage be significantly happier than my singleness?”. For some people (particularly undesirable people like me) singleness is not much fun. A lot of us are vary lonely and single against our will. Even a not so great marriage would be an upgrade for us, so we at least received a modicum of attention and appreciation. However for desirable people singleness is a lot more fun because they are wanted and appreciated. Marrying for them is often a step down.
The irony is that the people for whom singleness is significantly better than marriage are the ones people are trying to marry.