Hello again
The first thing I would do is make a pair of parallel straight edges at least as long as the bench top you will be making, shorter will lead to excessive hollowing, if you use it as a pivoting check
as well as visually.
Parallel, so having two edges which can be used as a reference, just incase they take a warp,
flipping one around will show twice the error should it have a bow,
Then you can check things like your bench top for instance, or make one master, since the work wont deflect on the bench, you don't really need that one dead flat.
If you can do that, or if you know you're bench is flat, then the test is if you can match some timbers together standing on edge without a gap (no pressing)
Sounds simple enough, but trouble might appear when more than one face is involved.
In my mind this is where a thicknesser shines, should it be accurate enough to do that test.
Can you achieve this, be it electron power or beans?
You're query wouldn't be of concern to me, as long as it's the most accurate.
I'd sooner focus on technique and all the rest, on a bench you are happy enough to plane on,
as I get the feeling you want this to be a tidy bench, and use the other one for rougher work.
You could do both if you liked, for experience doing heavy dimensioning and to give the thicknesser a break, and just use it for final skims, and see how well you did,
as I'm guessing it has a universal motor.
Personally, I think there is more to be learned when you don't have much material to play with.
Hope that makes sense.
Good luck with the build.
Tom