My future spouse follows a different religious understanding or practice. Is that a problem?

Differences in matters of furu' (secondary issues), such as school-of-law practices, can usually be managed, but significant differences in creed (akidah) must be weighed seriously.
Differences such as how qunut is performed, recitations in prayer or the practice of tahlil are recognised differences of opinion among scholars; a couple can respect each other. But if the difference touches on creed, or on an extreme ideology quick to declare others unbelievers, it can harm the children's upbringing and the harmony of the home. Discuss early: daily practices, the children's religious education, attitudes towards family members with different practices. If you are unsure about the creedal status of a particular teaching, consult the state mufti department. Allah calls the community to hold fast to His rope and not be divided (Ali 'Imran 3:103).