Hi guys,
Forgive me in advance. I've tried using the search function to look for this information and I just can't come up with it, so I'm going to ask straight out.

I'd like to install an engine oil temperature gauge, and I want to know what the users here suggest for installing the sending unit. The local parts store suggested I tee off of the oil pressure sending unit. I suppose it's possible the engine already has a fitting (or better yet a sensor) but my vehicle doesn't have any sort of printed manual I can buy. I've got a 2008 Toyota Sienna with the 2GR-FE 3.5L.

My Z31 300ZX turbo had an OEM oil temp guage. I wish all cars came with these.

VDO makes an oil temp sender that replaces the standard oil pan drain plug. I have never used one so I can't attest to the unit's quality.

The pressure sender/sensor location isn't really appropriate for oil temp readings. You'll be reading whatever heat migrates to the sender.

The pan plug is the right spot for the sensible use. Some Fast and Furious types on (I think) Mazda's (or whatever) seem to insist on some location that reads the cam supply, but that's just a matter of indexing. That is, there will be a corresponding sump temp that results in any localized temp in most usage most of the time.

Sandwich plate adapter... so you can measure at the filter.

I've got one of those cartridge type filters with a permanent housing. Would that work?

Back in my VW days I used VDO engine oil temp senders, the sump plug and the oil dip stick kind both worked great.

Nope, you're screwed... buy a new drain pan plug and drill and tap a temp sensor into that.