Short answer
Enough communication should take place to understand compatibility and important expectations while maintaining appropriate Islamic boundaries.
Islamic Guidance
What Islam teaches
The purpose of pre-marriage communication should be responsible decision-making rather than an unrestricted romantic relationship. Families or appropriate trusted people can be involved where useful.
Practical Guidance
What you can consider
Discuss important subjects clearly and respectfully. Avoid making major decisions based only on emotional attachment or a few conversations.
Sources
Qur'an 33:32; Qur'an 24:30-31.