My table build is in my signature, take that for what you will.
I have 5/8" holes on 12" centers. I really like it, but my table is 48" x 120".
I had a table that I built with 5/8" holes on 6" centers. They were cut in by waterjet.
For a table that small, I wouldn't bother with more than maybe 4 holes. Its not really big enough to warrant a full blown fixture setup. All you want is the ability to get a clamp on the inside of the table.
If you decide to put some holes in the top, I would skip the threaded holes, and go with 5/8" holes to utilize the StrongHand drop in clamps. They are cheap, and way, way faster than a threaded strap clamp set.
Simple rules for building a table:
Height is important. Probably more important than anything else. It needs to fit what you're doing. My tables are all 34" tall. It's a good height for me, I'm 6'3". I need to sit, stand, and build off my table. It seems to work well for all but very large frames, then I need to stand on a ladder or up on the table top.
Leave a lip around the top deep enough as the throat of your deepest clamps. 6" is usually perfect. That way, you can clamp all around the edge.
Be careful with wheels. They can be either a blessing or a curse. I have a forklift, so nothing has wheels in my shop unless I have made that decision to have a mobile table. On a table as small as yours, you don't really have the mass to keep it stationary when pulling hard, so I would think you'd want wheels. It would be handy to have a small table like that mobile.
Keep it simple. A tube frame base, bolted on top, and leveling feet or casters are all you really need. I have some features that I LOVE, but wouldn't work as good in a smaller table. I have receiver tubes under the top to insert vises and benders, but they rely on the table's weight to work. They won't work as well in a small, lightweight table.
YMMV, I've built a bunch of tables and benches, simple and complex.
