Hey theenpati,

I also believe that there shouldn't be issues about seats on a Sunday morning, but then reservations are also quite cheap... If you're not sure which train you'll be able to catch you can just reserve seats in two to be on the safe side.
In my opinion (and I'm tall), seats are quite comfortable and offer plenty of legroom in 2nd class , definitely much better than any eco-product of the major airlines. Just when you reserve seats at a table legroom can be restricted because of another person sitting across from you. So I would advise to reserve standard seats w/o table unless you're with three or more other people.
Another thing you probably already know: make sure to take an ICE and not an IC. Much more comfortable for almost the same price.
Enjoy Bari!

-txl.