N00b with some questions: TorquePro, newly purchased Prii with questionable service history

N00b here with a new-to-me 2010 Prius (Gen 3, right?). I've had it now for about 6 weeks. Got some questions.

The easy ones will probably be about my newly purchased OBDII reader & TorquePro.
With the understanding that I use this car for semi-long distance commutes daily, 45miles each way, with 95% of that distance spent at or above 70mph.

• 1. Which PIDs are most important to "watch" on a regular basis, which ones do you tend to have on your "main" live screen?
• 2. Is there a description of what a lot of these are, buried in the 20 pages of responses? I didn't see anything in the first 2-3 pages before I gave up.
• 3. Which PIDs would you suggest "logging" long-term? And is there a way to setup Torque pro to do so automatically, rather than having to hit the "record" button every time?
• 4. I note that the speed reported from Torque Pro is consistently 2mph lower than that shown on the dash, at all speeds as far as I can tell. Is this normal? I've passed by one of those road-side Radar signs that gives you a speed reading...and it matches what Torque says, rather than what my dash says. I've thought about adding the "GPS MPH" pid as well, to compare them, but haven't gotten a round tuit.

As to the rest...I begin to believe the service history wasn't kept up as religiously as I was lead to believe by the (Toyota branded) dealership that sold it to me. Yeah, I know...SHOCKING, right?

I had been losing on average about 1/2 quart of oil per tank-ful of fuel (so with my driving, about 1/2quart per week or so, see how I drive it & mileage/speeds above).

The first things I did were a can of BG 44k in the tank & going up a notch (to 5w-20) on the oil viscosity when I did my oil-change. Did those based on advice found on PriusChat. I was HOPING that the dreaded EGR valve/system cleaning wouldn't be required...as it's (probably) beyond my gear-headedness.

So far, after the above, my oil level has remained constant so I might have gotten lucky with an easy fix for that.

Anyway...When I changed the oil last weekend, it was HORRIDLY black and filter looked terrible. Which is what leads me to believe that the service history is...ummm...questionable. Also, the "locking clip" that is factory installed, theoretically to keep the filter-cap from spinning itself loose...was still on there & gave every impression of having never been touched. NONE of the "how to do an oil change" videos I watched even mention that clip, so I get the impression it tends to go away during the first service.

My fear is, at 130k miles, this might be the first oil-change this car has ever seen.

What else should I check on and/or watch for in the near future?

So far, the car runs smooth as silk, although the mileage is in the 39-40mpg range rather than the (near 50mpg) range I expected. A friend who has a Prius tells me that some of that is possibly down to my using it for lots of high-speed commuting, as he says I can expect to lose about a mile per gallon for every 5 miles over 50mph average. Truth in this?

Any advice is greatly appreciated.

EDITED to add a bit of context.