Just a curiosity as I bought my 98 Rodeo used (third owner): How often should the catalytic converters and oxygen sensors be replaced? Have searched and been unable to find any literature on this in regards to my model.

Replace them when they go bad.

Cat converters dont usually go bad unless there is a problem so no need to replace till then. O2 sensors can get weak but not set a CEL. I replaced mine around 100k miles. Runs a little leaner now and picked up 1-2 mpg.