Taking the train to Paris (Strasbourg)

Next month I have to go from Strasbourg to Paris on a Saturday. I haven't made my travel arrangements yet. Do I need to reserve in advance or is it easy to get a ticket for the high speed train just before boarding? I was checking the internet from here in New York, but I it seems you have to pick up your ticket at the station anyway, just before you board. Does it save much time to reserve like this?

Also, my husband likes the idea of first class travel, but I'm wondering if there is any reason to pay the much higher price, especially for such a short trip.

Thanks!
Betsy