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You don't need a wideband sensor, but it would be nice to have. It's not going to save you during WOT, if it goes real lean, real fast for some reason, you won't have time to react. Plus you can't watch the thing anyway.
Usually we're on the same page, but this is one time I have to disagree. My wideband lights up bright red when it goes lean at WOT. Saved my *** when one of my GT500 pumps was poorly grounded and my air/fuel spiked up to 17. Just seeing the bright red LEDs out of the corner of my eye told me to take my foot off of the gas before I spit a rod to the moon. It's a valuable safety net.
As for the passenger side catch can, skip it. I've never had oil in my passenger side line.
The passenger side line should be introducing air into the crankcase, not removing it, unless I'm mistaken. If I'm not, you wouldn't need an air/oil separator on that side, just on the driver side.