Doing the valve lash is relatively easy. You can test the clearance without making any adjustments, you'll just have to take the valve cover off. You wont hear it if they're out of adjustment. I mean , they might be out of adjustment and not make any sound or, they might be fine but you'll mistake the valve-tapping for injectors. Just open it up and test the clearance.

As for timing belt, you might as well replace the water-pump and all the belts while you have it apart. Also, you generally try to replace all the seals when you replace any parts.