"Wood move very little in the length. It moves most in the width (right angles to the grain). The wider the assembly, the greater the overall movement." Dave's right.
"apply any finish to all
surfaces" that includes, especially includes, the ends.
A 2' wide oak top could shrink and swell as much as 1/4" in extreme relative humidity conditions, a bar might be extreme.
You do not want to fasten top to plywood in any way. U may even want a slip sheet between them. Or don't use plywood at all. Let top rest on horizontal stretchers like a table top. There are everal shop made top fasteners that allow top to move. And fasteners you can buy.
If top can not move it will split. If edges are fastened, top will bow upwards, if glued down it will split top or plywood. When it shrinks back, split off chunks will prevent it from laying flat. If top shrinks it will split, possibly even open glue joints.
Biscuits will help align boards, but at times, being glued in can cause splitting. That's kinda rare tho. But use smaller biscuits, even #0. I have glued up panels, trying
to keep glue from biscuits, spritzing them with water , quickly inserting them B4 they swell and gluing up.
Shrinkage and expansion depends on moisture content of wood and humidity changes in room. There are online charts and calculators to figure that. here's one
Here are some ways to fasten top http://benchnotes.com/Fastening%20Ta...table_tops.htm
You should allow oak to rest in room where it will be used for several days to acclimatize, B4 building and finishing top.
Can you put a raised frame around top rim of bar? or will bartop overhang bar? A 1x3 with 3/8 or 1/2 extending above bartop Cut 3/8 to 1/2 deep groove slightly thicker than bar top 3/8 down from top edge of 1x. finished size of top should allow all edges to be half way into grooves all around. If 3/8 deep groove top should be 3/4 less than outside to outside of frame. slide top into grooves, do not glue. This is similar to raised panel cabinet door. Thicker frame would allow deeper groove allowing more movement. You could also cut an El shape frame instead of groove making a lip that extends inward. When fastening frame to bar but spacer between lip and bar top. Business card thickness will do.
Let us know when bar is finished and open for business. You gonna have some single malt back there?