IMO an OCC is not really required depending on your driving habits. Temp extremes and short drives can lead to more blowby than usual. The car has an oil separator and PCV valve, plus everything that
@ceric mentioned. Use engine oil that meets the OEM spec, and press the accelerator a little harder every once in a while to help the engine burn up some of the deposits. I had an 08 IS250 that should have been affected by carbon build-up, but I suspect my driving habits delayed it long enough for me to never have to worry about it.
Regarding warranty, I'm unsure if it voids it or not, but most of the time the OCC can be installed in a way that is easily returned to stock, in case you do need to make a claim. Because of this, I've installed a no-name Aliexpress OCC on my engine just as a redundancy. So far it hasn't caught any blowby on my 2.5 turbo, but others who installed OCCs have reported catching some blowby.
CorkSport sells an OCC. They come with instructions for installation. CorkSport also sells a
valve cleaning tool kit, but you'd need to contact them to see if it would work for the 2.5L engine.