Correct lathe height, according to what I've read or heard, is elbow
height for the particular operator. 3/4 MDF sounds insufficient to hold
up a lathe withour vibration, even if it cantilevers the base legs by
only a few inches. You could go with "2" by construction lumber (1
5/8"), tho. I made a whole stand of 2x12 and 2x6 with 3/4 ply sides,
works well and very stable.