As part of getting my '93 16v back on the road have decided the timing belt needs changing as I have no record of when (if) it was last done.

Looking at the various kits online they seem to come just with the belt and one tensioner.

Has anyone else changed any other bits at the same time - water pump or any other pulleys etc - while its half apart or have any tips?

Lad at the garage I use always recommends replacing the water pump while your there, infact like you said while it's apart get it done!

If you mean the 2-litre Sedicivalvole... isn't there a balancer shaft with a belt as well?

There is indeed - always best to change both!