What other components to replace w/timing belt?

RX300 with 120K, never had a timing belt. I see you can buy kits from Ebay that come with cam seals, pulleys, hydraulic tensioner, front crankshaft seal, etc. I know to change the water pump at the same time, but is it recommended or necessary to replace the other parts mentioned above while there? The parts seem inexpensive enough, but is wise to do?

Technically it's not necessary, but because there is some work in disassembling the front of the engine to change the belt, it is usually worthwhile to do it all at once. What would be worse than to change the belt only to find out a few months later you have to disassemble it all again for a leaking oil seal?

Those seals do age and harden, so replacing them with the belt is wise. Some people can skip replacing the seals at the first belt change, but would definitely do it at the second one. Not very difficult, but you have to be careful to not score or scratch the sealing surfaces around the shafts. I'd recommend it...as you say, they're inexpensive and saves labor from a leaker later on.

As for the tensioners, pulleys, and water pump, I would say it is not necessary unless they are showing signs of wear (noise, loose bearings, stretched springs, weeping coolant, or wet timing belt).

I've replaced the water pump in my Camry once, only for the reason that I had hit 200k miles, and the one I got had a significantly different impeller. It still works, but was disappointed I removed a pump with a nice stainless steel one for a cast iron(?) one.

Hope this helps!