I can definitely appreciate the beginner phase thing. We’ve all been there. I still stand by my recommendation to kit use them although the HTD line is better than any polks before it. If you really are determined to use Polk due to the discount, I would use four HTS12’s. Still leaves a lot on the table but that’s what the beginner phase is for!
And if you can, definitely move the heights forward of the LP. In a x.x.2 system, that’s where they are intended to go. In that big space, imo you should have at least 5.1.4, and definitely have room for 7.1.4. In a .2 system since there’s only two height speakers, all of the height info gets sent to them. If you have .4 or .6 heights, you get front to back panning, plus the XYZ placement of objects(if the track uses them). I digress...
For you, I’d shop for big boy subs, or use at least four polks. And move the heights up.