will there be any differences at all between marriage now and marriage in the messianic era, or no?

In general, the Torah laws are eternal and not subject to change. On the other hand, the Sanhedrin has very far-reaching powers, and if, when revived, they see a need, they can institute significant changes, sometimes permanently or temporarily- either short term or long term. Some have thought of reading into the verse in Yirmiyahu 31, 21, that in the messianic era there may be some changes, but there are so many other, more simpler ways, to understand that verse, especially when seen in its context, that it's totally inconclusive.