I think you subconsciously already know the answer.  Here's my
reasoning.

The most basic and inarguable rule is that the  *total* weight of
everything, including the various  carriers as well as the tare weight
of the cargo, can't exceed the rating of the weakest link.

The excess-cargo platform is what would worry me, more as a dynamic
than a static problem.  The effect on handling (as well as the stress
on the hitch and the attachment points of the car when things start
jouncing around at speed) is a function not only of weight but of how
far back there it is cantilevered.   You'll also be sacrificing a lot
of real-world road clearance.    Both could be issues for  a none too
huge and rather low-slung car.   Those things are IMHO really best
left to pickups and SUVs.

I'd skip the excess-cargo platform and the dual adapter, instead
looking into a roof-rack clam (the places that sell bikes and
accessories usually have a variety) or a  luggage rack for the trunk
lid as places for some (lightweight) extras. That would mean there's
no need for the dual adapter, and then no need for the 1.25" to 2"
adapter, and you can just go with the 1.25" incarnation of the Allen
rack. (Unless you already have its 2" version.)

Having driven round trip SF-Portland in an '03 Grand Am with a lot of
stuff, I have a lot of respect for it as a car, but an acute sense of
its limitations as a truck!

One man's  opinions, worth what you paid if your connect time is
cheap,
--Joe